Not sure where to post this - foster care question

A

Is anyone familiar with how to go about it when a situation involves the children being taken from their father (custody was never set but mother has been on drugs for a while so they can’t be placed with her- parents are still married but separated) and placed into foster care, but there is family in another state willing to take the children? Dad isn’t supportive of it, he wants them in that state or somewhere with his family who has not yet taken them, also can’t get a clear answer as to why. Not sure if mom has a say, trying to contact her. It’s been a mess. We have a niece and nephew that have been placed into foster care. Their older sister said that they are with a family she doesn’t know, dad is trying to claim that they are with their grandma and that’s where they want to be. We are just trying to get answers and I have no idea where to start. I have a 3 bedroom home, a good job with excellent benefits, and can provide for them until they can return home. My boyfriend is afraid that they will end up lost in the system with how much of a mess both parents are. We are so lost and don’t know where to begin

Update: we also just found out that they are actually in foster care in Arizona. They lived in Colorado so we have no idea how this happened, if their dad took them there and then lost them or what