2 and 4 yr old brothers w/ RAD- Help! Vent and Questions...

Here's my story. My hubby and I were placed with a 2 day old baby a year ago and we still have him. His older brothers are now 2 and 4 and have been bounced around and are now in their 3rd foster home. I thought I had made it clear to my CW that we would take them if there was ever a need, but unfortunately, they kept getting "moved" and we would not find out until after the fact. When I asked my CW about it, she would say that she didn't want them disrupted again so they would stay where they were. :( Today I was contacted by placement to ask if I would take my fs's brothers because their placement was "falling apart." Yes!! I'll take them. Later I got off the phone with their current foster mom and she tells me the 4yr old has RAD symptoms! Though that is a little intimidating, I'm committed to these kids! So here it goes... I'm very happy to take my fs's brothers because I want to have them together in the same home and I want the opportunity to love on these boys. RU is expected for the 2 and 4 yr old within the next couple of months. My 1 year old is a half sibling and is going toward TPR. But I'm frustrated with the current foster mom!! Why couldn't she just stick it out for a couple more months so these little boys wouldn't have to transition AGAIN!!!??! AND I would love any advice ya'll have about RAD. I'm familiar with it through reading and discussing, but have never had a child with it. I'd love any advice you can give me!