Why would someone want the children if they didn't know them? Is it a sense of family obligation?
for me....as much as i'd like to think, as an adoptive parent, that biology doesn't matter.....biology does matter. if there is a chance for a child to be with a relative that is appropriate, that is usually what the courts will choose also. the aunt's situation doesn't sound ideal...but i've seen less ideal situations make a 180 at the last minute and end up with the children. i know it is not what you want to hear....but it is true. we are non-related realtives...which basically means a son we adopted previously is related to the new baby. we chose to adopt the new baby because there is really no reason that these brothers should not be raised together. i think there was a little sense of obligation, like i owed it to these kids to keep them together....but that was about it for me. i know in my heart that if they called me tomorrow about another one, i'd feel the same way. i'd have a harder time if they had been in their foster home for longer than 6 months and bonded....but in the end, i'd really have to weigh what was best for all the children in the end.
The kids would move to the other side of the country leaving everything they know.
i just did this....granted a is only 9 months old so he isn't fully aware of the move...i know others here have adopted older children.
Why put the children through that if there was no bond there already?
because it has to be what is best for the children in the long run. it is such a horrible situation for everyone, and i'm so pro- don't move a kid, that it makes it even more difficult......but i acknowledge that if there is a chance a child can be placed with a relative, even one they barely know, it is still probably the best situation.how long have they been with you?
Yes, I'm hurting for me at the possibilty of loosing them, but also I worry about them.
i know. it is hard to love other people's children as your own, and then have them leave. i did it once....i vowed to never do it again....it is absolutely heartbreaking and you have every right to be hurt and upset. it doesn't matter how many classes you take as a foster parent that tell you to be prepared for this....it is still worse than you ever expected it to be! 
I understand why in the eyes of the state family gets priority, but why fight for them if you don't even know them?
that's hard to explain. but the second i knew my child had a brother....i knew they had to be together and that there was no sense in them not being together so that the baby could be raised by a non-family family. my other thing is that i have other adopted children from a different family, that were older when they were adopted by us. they would have given their right arm to be with a family member.....regardless of who they were and how bad the situation was even. i've seen them struggle with so many problems and i'm sad that they not only lost their parents, but their cousins, aunts, grandparents, etc....and not just the ones they knew, but the ones they didn't, or only knew casually. i think it is alot for a child to lose....so if they have the option of remaining in contact with one or some of those people, i think it can be a good thing for them.
Although I know you do not know these people any insight would truly be appreciated. Is there anyone who has seen children thrive through this kind of situation? I just want to better undestand.
i think there are lots of different situations where children thrive in families. i think they can thrive both in a fost/adopt situation and a relative placement situation. please just know it is hard on all sides......and i've been on both. know that for the relatives...sometimes we do know about the children but it takes SOOOO Long to get the social worker started on our paperwork to even allow us to contact the foster family or visit the child. i've heard of some relatives that call and call the sw and the sw tells the relatives they have to wait until tpr before anything is done...and then that leaves a child in a foster home for 2 years before the relatives are able to step in.
my heart goes out to you. i'm sorry. it is a very very sad thing to watch a child you love leave your home. nothing i can say will make that better, and i'm sorry about that. it doesn't matter if the child goes to a perfect relative and they will have an amazing life with a loving family member....it will not diminish the pain you feel. it will hurt, and it will hurt for a while. that being said, don't give up yet....there are also plenty of relatives that don't follow through or are not approved and in the end the foster family adopts those children....i have 3 of those. 
it is a rollercoaster....just hang on tight!