Can a sorcerer Twin a concentration spell?

Yes, as long as the spell qualifies. 

For example, a Divine Soul could not twin Bless, because that spell has more than one target. Similarly, any sorcerer could not twin Hold Person when cast above second level, because that makes it target more than one creature.

You could, however, twin spells like Haste, Polymorph, Greater Invisibility, or Disintegrate. Whether or not the spell is concentration has no bearing on the Twinned Spell metamagic option.

I'm assuming that if you lose concentration, both instances of the twinned spell dissipate?  It's not like each instance has its own check to maintain concentration, right?

Correct. Similar to how a Bless can target multiple people, but all effects are lost when the caster loses his or her concentration.

Yes.  If you twin haste, for example, if conc gets broken /both/ of the targets will lose their action.

If you twin-spelled polymorph could you make one person a bronze dragon and the other person a green dragon or do they have to be morphed into the same creature?

Quote from Fergiesaur >>

If you twin-spelled polymorph could you make one person a bronze dragon and the other person a green dragon or do they have to be morphed into the same creature?

 1) Polymorph can't change creatures into other creatures except for beasts, so i'll go with true polymorph.

2) I would say that you can choose only one form per casting of the spell, meaning that you could only turn them both into green dragons, or both into bronze dragons.

It's worth remembering Twin Spell does not cast the spell on a second target. You cast the spell once. The metamagic just adds a second target. You're still only casting it once, maintaining concentration on one spell, and choosing the effects of the spell, where choice is given, once. The spell's effect just now targets 2 instead of 1. That's it.

Aight, can we twin Wish?

Nope. Has to have a target. Technically, wish itself has no targets.

Could a sorcerer do the following sequence

1. quicken cast mind sliver targeting mob 1

2. Twin mind sliver to mob 2

3. Regular cast mind sliver on mob 3

4. Twin that one to mob 4

4 sorcery points I think 

If you cast a spell as a bonus action you can’t cast anything other than a cantrip as your action.

Quote from Areon_Valehn >>

If you cast a spell as a bonus action you can’t cast anything other than a cantrip as your action.

Mind Sliver is a cantrip, but you can't apply quickened and twinned to one spell.

Quote from Fergiesaur >>

If you twin-spelled polymorph could you make one person a bronze dragon and the other person a green dragon or do they have to be morphed into the same creature?

 Are we gonna ignore the evil threadcromancy going on here lol?

Quote from EddyJ >>

Yes, as long as the spell qualifies. 

For example, a Divine Soul could not twin Bless, because that spell has more than one target. Similarly, any sorcerer could not twin Hold Person when cast above second level, because that makes it target more than one creature.

You could, however, twin spells like Haste, Polymorph, Greater Invisibility, or Disintegrate. Whether or not the spell is concentration has no bearing on the Twinned Spell metamagic option.

Just for clarity you technically can't twin disintegrate because it targets objects, some tables disregard the ruling but that was the ruling

Quote from Great_Axeblade >>

Quote from Fergiesaur >>

If you twin-spelled polymorph could you make one person a bronze dragon and the other person a green dragon or do they have to be morphed into the same creature?

 Are we gonna ignore the evil threadcromancy going on here lol?

That would be minor necromancy(I categorize replying to a post at least five days later with little chance of a reply Spare the Dying(A necromancy cantrip), three months Animate Dead(A third level spell for three months), and six months Create Undead(Sixth level spell). Those are the main categories.

Quote from Halfastbracegirdle >>

Quote from Great_Axeblade >>

Quote from Fergiesaur >>

If you twin-spelled polymorph could you make one person a bronze dragon and the other person a green dragon or do they have to be morphed into the same creature?

 Are we gonna ignore the evil threadcromancy going on here lol?

That would be minor necromancy(I categorize replying to a post at least five days later with little chance of a reply Spare the Dying(A necromancy cantrip), three months Animate Dead(A third level spell for three months), and six months Create Undead(Sixth level spell). Those are the main categories.

 Spare the Dying is more of "I'm going to keep this thread from dying" than "I'm going to necro this thread."

It is worth noting that thread necromancy is perfectly fine if you are contributing something worthwhile to the discussion. The mods have recently decided to be even more lax about this. 

The post I was referring to was 14 months apart. feb 2020- april 2021. This is Resurrection.

Quote from Thauraeln_The_Bold >>

Quote from Halfastbracegirdle >>

Quote from Great_Axeblade >>

Quote from Fergiesaur >>

If you twin-spelled polymorph could you make one person a bronze dragon and the other person a green dragon or do they have to be morphed into the same creature?

 Are we gonna ignore the evil threadcromancy going on here lol?

That would be minor necromancy(I categorize replying to a post at least five days later with little chance of a reply Spare the Dying(A necromancy cantrip), three months Animate Dead(A third level spell for three months), and six months Create Undead(Sixth level spell). Those are the main categories.

 Spare the Dying is more of "I'm going to keep this thread from dying" than "I'm going to necro this thread."

It seemed the most relevant necromancy cantrip.