Yikes, that is indeed a stressful and frustrating situation
I guess both B1 and B2 know that you have another offer with a deadline of April 15 right? If not, then my answer to your earlier question of "should I ask them to expedite my application", is yes, especially for B2.
Sorry if I keep asking the same Q, but did you ask School A (the CGS school that already accepted you) for an extension beyond April 15? It seems like if you ask for May 3 or something, that will give you at least a day or so after School B2 releases their decision in order to decide between A or B1/B2. Like I said above, if School A says no now, you could consider asking again closer to the deadline because maybe by then, they would have received enough decisions from candidates that they wouldn't care if you said yes or no so they won't mind waiting until May.
Otherwise, you have the tough choice of a sure thing that's not your top choice vs. a chance at your top choice. It's up to you if you want to take the risk of potentially burning a bridge at School A. Or, perhaps School A won't promise you a spot after April 15, but they might say that you might still have one even if you accept in May as long as the spot is still available. So you could ask School A what happens if you can't decide by April 15---does the offer expire or is it simply that the spot is no longer a sure thing?
If it helps to know, this is a common problem in both academic and non-academic workplaces. It's really tough to make decisions when you have deadlines that don't line up, but we'll have to make these decisions.
