Plane shift has two uses:
- to bring yourself and up to 8 more willing creatures to another plane, or
- to make a melee spell attack against a single unwilling creature, and then force it to make a Charisma saving throw or be brought to another plane
The sorcerer's Twinned Spell metamagic option lets you spend sorcery points to affect two creatures with a spell that normally affects only one.
But here, I'm not sure if the second effect of plane shift is considered eligible for the Twinned Metamagic, because its first effect can indeed affect more than one creature.
Can Twinned Spell be used on plane shift when it's used to banish an unwilling creature to another plane?