another question

[Mamacass]

I've heard that my brother and his wife are talking about a divorce, but I'm not supposed to know this yet.  They have 3 girls, and honestly all 3 were an "oops" for my brother but were planned by his wife.  I know that sounds lame since it happened 3 times, and my brother does feel like it's partly his fault but it's a long story and not really important right now.
Anyhow, I don't know that my brother will want to keep the girls.  He is going to be buying the shop he works at, and he just doesn't have a lot of time.  And like I said, he was upfront about not being ready or wanting more than one kid.  His wife is a mess.  She doesn't work, b/c she could never qualify for a job making more than minimum wage (and even that is difficult for her).  She doesn't clean the house or cook dinner.  They have to eat out all the time.  My brother cleans the house every couple months (like serious deep clean).  The kids go days without baths, and one is currently failing kindergarten.  The older one is in 2nd grade, but only b/c she has been placed each year, not because she passed.  My SIL honestly can't help with the school work b/c she is not very educated.  
So now that I've told the background (at least the short of it), here's the issue.  If they get a divorce, and my brother isn't willing to keep the girls, I want to take one of them, and my sister wants the other 2.  Neither of us can take all three b/c the middle one has autism (although my SIL won't admit it),the baby is a handful, and we both already have kids.  
Is this even possible, for us to get custody of these girls?  I know if they stay with their mom they will end up high school drop outs and sluts.  They are such beautiful and amazing girls and I know my SIL is not capable of raising them.  I know that it would be better if we could keep them together, but my sister and I live a few miles from each other, and hang out all the time so the girls would still be very close.  
Any suggestions?  Please be honest.  I'm going to mention this to my attorney in a few weeks, but we have lots of other things to discuss about our upcoming trial, so I know we can only really discuss it in passing.  

[Giggles]

that unless you have the BM's approval of this, it probably won't happen.  Unless your brother can pove to the court that the BM is totally unfit, gains SOLE custody and then assigns you and your sister guardianship??  That might be a way to go??