Foster care and TTC

My sister's ex husband (and the father of her two children) has a son that is 19 months old with a different woman. She (the other woman) has 4 other children from a previous marriage as well. Well, long story short, they had charges brought against them for child abuse and all of her 4 children were removed from her care for abuse (investigation is still pending) this will be the 3rd time the mother has lost them for this. CYS allowed them to keep the 19 month old while they investigate (why? I have no idea) there are physical marks on all children except the 19 month old. Well, I was asked if anything happens if I can take the boy into my care, my 13 year old nephew begged me, because it's his brother. I feel like I can't say no. I would love to help, but I'm unsure what all questions I should ask. What do I need to be prepared for? The little boy is a week younger than our son so we are set in that department. We have two of everything already (except cribs but we can get one)
Also, this will stop us from TTC baby #2 right now (my husband doesn't think we can take on two the same age and an infant.) I feel selfish not wanting to stop but I want the little boy safe and to have his siblings.
So we have A LOT. Of talking to do. This seems like the decision would be simple, help the child, but what about when they get him back after we have grown attached? What about us being left worrying about a child we cared for going back to a home like that? There's a lot more to it than one would think, you know? 
I'm a SAHM right now, I left my job about a month ago. So, I have the time, we have the room, we have the means. 
Any help would be appreciated. If you need more info just ask, I'll be sure to fill you in with what I know.