On the one hand, state workers typically really REALLY hate it when it feels to them like someone is trying to usurp control in an area that they feel like they should have control. They really really don't like foster parents making placement plans for kids.

Now - if he were aware of someone who wanted to adopt and who he is friends and neighbors with - that would facilitate contact between siblings - then he could suggest that to them. And depending on who the worker is, they may consider it or they may not.

But there's really no way to take control of the situation - and definitely no way to take control of the decision making. The best hope is to perhaps have some input/influence.