You attack, and the spell transmits the attack to a creature within 5' of where the gaze target is (because for the purpose of the spell, you count as being in that space).
I do not think you have interpreted it correctly as there is nothing about 5'
...you can cast spells as if you were in your space or the other creature’s space if the two of you are within 60 feet of each other.
There is nothing about melee physical weapons. If you cast a weapon buff, it cannot be on your weapon as your weapon is not there.
I'm going to use a different spell entirely as an example of why this doesn't work.
Flame Blade conjures a blade of fire in your hand. It also gives instructions on its use: As a Magic action, you can make a melee spell attack with it. However, the spell's effect is limited to creating the blade. You can't treat the blade as being in the other space, and you can't grant it to another creature. It must be in your hand.
Booming Blade hits a similar snag. The spell has effects that are attached to the melee weapon attack. However, the target must still be within 5 feet of the melee weapon in use. The magic could transfer, but the physical attack cannot because the Gaze doesn't move anything but the actual magic through the connection and that attack isn't part of the magic, it's part of the activation.
(Also, the flavor of Steel Wind Strike is you run really fast between targets and hit them in melee. But the mechanics are you just hit them from up to 30' away with your hand or the weapon you use as the M component, or whatever, it doesn't actually matter, because it is still a melee attack. And there's no question that you could cast SWS from the location of your gaze target, even if you were inside a locked room that you could not get out of, so long as you were within 60' of the Gaze target).
Running really fast between targets is one valid interpretation of the flavor, sure, but not the only. It only says you vanish, make the melee attacks, then reappear either where you were or within 5 feet of one of the targets. There's no requirement that you have to strike them with the weapon, so Steel Wind Strike isn't relevant to the discussion at hand anyway, it's 100% different from the discussion's situation.
You attack, and the spell transmits the attack to a creature within 5' of where the gaze target is (because for the purpose of the spell, you count as being in that space).
I do not think you have interpreted it correctly as there is nothing about 5'
...you can cast spells as if you were in your space or the other creature’s space if the two of you are within 60 feet of each other.
There is nothing about melee physical weapons. If you cast a weapon buff, it cannot be on your weapon as your weapon is not there.
... "You brandish the weapon used in the spell's casting and make a melee attack with it against one creature within 5 feet of you."
And It's not a weapon buff. It's a spell that makes a melee attack within 5' of you. (Except with gaze, 'you' are where the gaze target is, so within 5' of that). It never limits it by reach, and indeed, the spell overrides and replaces the weapon's reach with the "within 5 feet" instruction. It only gets weird with Gaze, because replacing weapon reach with 5' when that's far from your physical body is strange, but not so strange as not to be explained by 'the magic did it'.
Again you still are not interpreting the Gaze rule. You don't make a melee attack as the the Gaze is to allow the origin of a spell be from another living organism. If the spell is with a weapon it does not work. The living subject has to be the one that makes the melee attack. That is why using your own words it "..****y gets weird" is happening. The Gaze is for Eldritch blast or dissont whispers or phantasmal force or the none warlock spells like magic missile or fireball. The way you are describing a melee attack spell, is not going to work.
The spell origin is at the subject, but the melee attack is not you, it is the living subject.
If you have Gaze of Two Minds active on your ally, call them X.
1/ If you cast a cantrip like booming blade, can you make a melee attack against a target adjacent to X? (Because the "within 5' " overrides the weapon's reach, and the attack is part of the spell?) True Strike? (Doesn't have the 5' range specification, but the attack is still part of the spell? -- I'm thinking the lack of the range specification is key) If yes with True Strike, what about True Strike with a ranged weapon - would the ammunition fire from X's position?
Best guess: Yes (booming), no, no
If you're a Warlock/Rogue multiclass and at least one of the melee options works, do you get sneak attack dice? (Because X is adjacent to them?) Best Guess: yes.
2/ If you're invisible from hiding and cast a spell (without verbal components) with an attack roll originating from X's position, do you lose invisibility because of the attack roll? More interested in RAI here / logic of what the rules are intending to represent. (RAW is obviously yes, but it's silly.)
3/ Even when not unseen or invisible, should you get advantage when casting a spell with an attack roll from X's position? (because they see/hear you casting the spell, but then the spell originates from somewhere else?) Only the first time? (unless you change who you're 'gazing' through?)
4/ If X is unseen/invisible, but you're visibly casting a spell with an attack roll, do you gain advantage when it originates from X's position? Does it affect X's invisibility? (I'd think no on the latter).
5/ If the enemy cannot perceive you casting the spell, they can't counterspell it when it originates from X, right? Because X isn't spellcasting?
1. Generally I say no. That being said I can see an argument for if X is armed casting the spell from their location would trigger it on their weapon.
2. yes, making an attack whether its from a spell or a weapon breaks invisibility.
3. GM call, you don't automatically but giving advantage for trick maneuvers is allowed.
4. Same as 3 imo. If you are both unseen its clear advantage. And no impact on their invisibility.
What doesn't?
I do not think you have interpreted it correctly as there is nothing about 5'
There is nothing about melee physical weapons. If you cast a weapon buff, it cannot be on your weapon as your weapon is not there.
I'm going to use a different spell entirely as an example of why this doesn't work.
Flame Blade conjures a blade of fire in your hand. It also gives instructions on its use: As a Magic action, you can make a melee spell attack with it. However, the spell's effect is limited to creating the blade. You can't treat the blade as being in the other space, and you can't grant it to another creature. It must be in your hand.
Booming Blade hits a similar snag. The spell has effects that are attached to the melee weapon attack. However, the target must still be within 5 feet of the melee weapon in use. The magic could transfer, but the physical attack cannot because the Gaze doesn't move anything but the actual magic through the connection and that attack isn't part of the magic, it's part of the activation.
Running really fast between targets is one valid interpretation of the flavor, sure, but not the only. It only says you vanish, make the melee attacks, then reappear either where you were or within 5 feet of one of the targets. There's no requirement that you have to strike them with the weapon, so Steel Wind Strike isn't relevant to the discussion at hand anyway, it's 100% different from the discussion's situation.
... "You brandish the weapon used in the spell's casting and make a melee attack with it against one creature within 5 feet of you."
And It's not a weapon buff. It's a spell that makes a melee attack within 5' of you. (Except with gaze, 'you' are where the gaze target is, so within 5' of that). It never limits it by reach, and indeed, the spell overrides and replaces the weapon's reach with the "within 5 feet" instruction. It only gets weird with Gaze, because replacing weapon reach with 5' when that's far from your physical body is strange, but not so strange as not to be explained by 'the magic did it'.
Again you still are not interpreting the Gaze rule. You don't make a melee attack as the the Gaze is to allow the origin of a spell be from another living organism. If the spell is with a weapon it does not work. The living subject has to be the one that makes the melee attack. That is why using your own words it "..****y gets weird" is happening. The Gaze is for Eldritch blast or dissont whispers or phantasmal force or the none warlock spells like magic missile or fireball. The way you are describing a melee attack spell, is not going to work.
The spell origin is at the subject, but the melee attack is not you, it is the living subject.
1. Generally I say no. That being said I can see an argument for if X is armed casting the spell from their location would trigger it on their weapon.
2. yes, making an attack whether its from a spell or a weapon breaks invisibility.
3. GM call, you don't automatically but giving advantage for trick maneuvers is allowed.
4. Same as 3 imo. If you are both unseen its clear advantage. And no impact on their invisibility.
5. yes.