How To Transfer Guardianship From Previous Guardians?

Location: Utah

My husband and I went through the steps of becoming licensed foster parents in hopes of gaining custody of my nieces and nephews 6 years ago. Only the youngest boy is biologically related to me, not that it makes one iota of difference imo. From the moment I met them I claimed them as family and treated them with kindness and love.

However, the judge disagreed and decided to place them all with the maternal grandfather and stepmother as there was more blood relation and a longer established relationship. Both bio mom and dad wanted them to put with us but the grandparents were given full custody by the courts and the parents were ordered to pay child support. The children were not adopted.

Fast forward to now, the older ones have left the nest. The grandfather is emotionally and physically abusing my nephew as he told me himself. He says he's done with my nephew and we can take custody immediately or he's putting him back into foster care.

I am desperate to get my nephew out of this situation ASAP by any means necessary. We're supposed to meet up to discuss transferring him into my care.

Is there a legal way to just have the grandparents sign there rights away? Or would it have to involve a judge as the parents are ordered to pay child support (not that they do and I don't care about the money)?

If it matters both bio mom and bio dad realize that they do not have the means to care for him still and they would prefer he's placed with me until 18. They want him out of there immediately.

Is there anyway we can transfer the custody without the courts?

*Also if the grandparents reneg I plan on immediately opening a case with CPS and law enforcement, due to Utah being a one party consent state for electronic recordings