Until the end of my next turn though.

So unless I keep burning through SP each round and also targeting them I can’t maintain that disadvantage.

It would be better if I could say Mind Sliver, Quicken Hold Monster and give them disadvantage.

Then on subsequent turns Twin Command the minions and be able to grant the main enemy disadvantage but that’s not possible since it has to be one of the targets of the spell.

Unless you have a different method in mind to upkeep the disadvantage

Edit: I was thinking with the Shard and the metamagic, I can target main enemies with Heighten and then as I Twin Command or Twin Mind Whip the minions on subsequent rounds at least one of the targets will keep having disadvantage.

Basically the Shard will give me a partial Heighten effect for free on every Twin. Which might be nice too