I have twin girls (freshmen) who are at 2 different schools. They are fraternal, have shared a room, best friends and worst enemies. I will say that each one has grown in ways I don’t think would have been possible if they went to the same school. They FaceTime a lot. They missed each other a bit more their first semester. Personally if they go to the same school I would let them set their own boundaries. That way you’re not responsible for the outcome, they are. I would think the girls working it out before either one commits would be important.
For parents who have twins junior or below in HS I suggest you have this conversation when they apply. Mine decided to apply early to separate schools so this never came up 
@wisteria100 She was interested but we figured because she was deferred it was almost the same as a no, so she has not been counting on it. However – she just got accepted there a few minutes ago, so that may still be the first choice after all! We haven’t seen financial aid from the ED school (although I’m sure it’s fine because we got a pre-ED estimate from them) and there’s a lot to talk about, but good stuff.
@NCmom14 We did have the conversation when they applied…honestly as they’re such different people this was the only school that appealed to both of them and I didn’t have a problem with them both applying, especially as D2 was applying ED to a different school and had a lot more on her list. It was a “perfect storm” of bad overnights at some of her accepted schools, getting deferred, etc, that led to this situation. And to be honest, I never thought D2 would end up seriously considering a school that’s not co-ed. Live and learn.
We are now in a happy fog because D2 got into the ED school, but there are many conversations still to be had. I’m super happy for them both.
Well, there was this set of twins I went to school with (forget identical, we’re talking copies) one in Mechanical and one in Electrical Engineering… Even their close friends couldn’t always tell them apart. There were lots of rumors floating around about them, especially since they never took core engineering courses together (i.e. brother A was the Math guy, and B was the Physics guy). They both graduated with near 4.00 and got admitted to the same top 10 grad school…
We did have a few sets of brothers/sisters in the same school and nobody thought much about it, I don’t see why twins would be any different.
In a big school being together would not be much of an issue. My girls are a few years apart but I would love it (they too) to be together. Not going to happen due to wildly different majors…