To put it simples, i have two questions about familiars:

1- Can familiars be targeted by spells like Bless?(And for the same matter, Bane and others likewise and be affected by them)

2- If a familiar is in the same space as a Friendly Medium size creature(lets say, a Sprite on a creature's back or shoulders), can it gain any bonus to AC, like if it was affected by half cover or three-quarters of cover?

Edit: This one is not related to familiars but 3- If Rolling for an attack or saving throw while affected by a spell like Bane and the result of D20 - D4 equals to a negative number like -2, do we consider exactly that number or do we consider a minimum of 1?

Quote from pablogabreup >>

To put it simples, i have two questions about familiars:

1- Can familiars be targeted by spells like Bless?(And for the same matter, Bane and others likewise and be affected by them)

2- If a familiar is in the same space as a Friendly Medium size creature(lets say, a Sprite on a creature's back or shoulders), can it gain any bonus to AC, like if it was affected by half cover or three-quarters of cover?

Edit: This one is not related to familiars but 3- If Rolling for an attack or saving throw while affected by a spell like Bane and the result of D20 - D4 equals to a negative number like -2, do we consider exactly that number or do we consider a minimum of 1?

1.  Yes.
2. I'm not sure I understand this one, so I'll just be explicit.  Suppose your familiar is a tiny owl:
   1. If it's entirely within your pocket, it has total cover.
   2. If it's peeking out your button-hole, it has 3/4 cover.
   3. If it's sticking its head out of your pocket, it has 1/2 cover.
   4. Note that in none of these positions will a sane DM let the Familiar take the Help action for anything physical.
3. Same answer as for a static modifier, like 1d20-1: there's no minimum.  You can roll 0 (or less) on the roll.  This typically won't matter, as typically nothing in the game has a DC below 5.

1) Yes, a summoned familiar is a creature and a valid target of spells and attacks.

2) Technical occupying the same space as another creature, even a friendly one, is not allowed RAW. As for cover, yes a creature can grant another creature cover if they block half or more of the target from the attacker.

3) I can't think of a situation where this distinction would be relevant. I don't believe it is possible for a target's AC to be made low enough for a total of 1 to hit, but a total of 0 or less to miss. With attacks though a natural 1 always misses and a natural 20 always hits and is a critical hit, regardless of the actual total and the target's AC. Saving Throws and Ability Checks only care if the total meets or exceeds the DC. But again I can't imagine a situation where a DC would be 1 or lower. In such a situation a roll probably shouldn't have been called for at all.

1. Simply Yes, familiars are creatures.
2. If they are considered mounted, no AC/cover. If they are in your backpack or something, then they would have cover from that.
3. The lowest that can be rolled after all modifiers is 0. Rarely matters, 0 is never passing so being less than 0 doesn't change that.
   • For example if you roll a 1 on the d20, a 4 on the d4 (for bane) and have a +3 modifier, you rolled a 0. If the modifier is +2, still 0, if the modifier is +4, you rolled a 1. Like that.

A familiar is a creature and follows all the same rules as any other creature regarding cover or whether or not it can be targeted by a spell.