How could some parents be so selfish?

So, BIL's BM went to jail for two years and decided to give her now bf custody of the kids that she and BIL have together. We just found out that the bf's a drug dealer from her mom. So, we're taking our vacation time this week to go down there and see if we can get the kids and bring them home with us. My BIL isn't in a stable home, but I know how this girl thinks. She didn't want him having them at all. I've lived with this girl, and it's not just as simple as him not being able to provide a stable home for the kids bc she kicked him out. She's a biotch and no one can stand this girl. We all wonder what is about her that's got bil all twisted about her bc she's nothing but bad news. I'm just peeved about the whole situation and pray that my DH and I are able to bring the kids into a stable home.