Edit: Never mind any of this. I just realized that Twinned Spell's range requirement (the second creature must be in range) makes this not work. The range of gate is only 60 feet.
Twinned Spell: "When you cast a spell that targets only one creature and doesn’t have a range of self, you can spend a number of sorcery points equal to the spell’s level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip)."
Gate: "You conjure a portal linking an unoccupied space you can see within range to a precise location on a different plane of existence. ... When you cast this spell, you can speak the name of a specific creature (a pseudonym, title, or nickname doesn't work). If that creature is on a plane other than the one you are on, the portal opens in the named creature's immediate vicinity and draws the creature through it to the nearest unoccupied space on your side of the portal."
From the Sage Advice compendium: "If the two of you are curious about our design intent, here is the list of things that disqualify a spell for us: • The spell has a range of self. • The spell can target an object. • The spell allows you to choose more than one creature to be affected by it, particularly at the level you’re casting the spell. Some spells increase their number of potential targets when you cast them at a higher level. • The spell can force more than one creature to make a saving throw before the spell’s duration expires. • The spell lets you make a roll of any kind that can affect more than one creature before the spell’s duration expires."
None of this offers a really ironclad answer, but none of the disqualifiers seems to apply to gate, so it would be fair to say you could do this. The question then is, do you get two gates, or do you get one gate which can suck through two creatures? My general interpretation of Twinned Spell has been that it duplicates the effect as necessary--if you cast fire bolt and twin it, you get two blasts of fire, not one blast that bounces off the first target and shoots away to the second.
However, Twinned Spell doesn't actually say that! It just says you can target a second creature. And the wording of gate makes the choice of target separate from the creation of the portal.
I don't have a clear "Here is the Word of RAW in black and white answer," but based on the above, I would say you can target a second creature but you only get one portal. The second creature must be close enough to the first that the gate can pull it in. Otherwise it isn't "in range."
