That seems to be the consensus of my roommates, as well. (No, before you ask, my roommates are not Legion. If only.)
Yeah, because you've already got Tali & Garrus, there's no more room in your squad. 
Pfft, tell that to my 7-member squads in Titanomachy. xD
Well you're sharing living space with them and some other people, you can't possibly be able to fit much more than that. 