Multiple phones under one apple ID-help.

I have multiple phones under one Apple ID. I'm trying to figure out how to make it family sharing instead. I can't get my daughter's phone to not be the main one. I need to switch it to my phone and then figure out how to create family sharing. I don't want to create an id for each phone because they won't have the songs they have already downloaded. What is the best way to switch these phones to family sharing under one apple ID.