Toying around with the idea that Gedomaru was originally spawned by RALRO, as a sort of personal project to try to create life from thin-air (though Jebediah would be the first to master life making in its purest form through Altana crystals with Sunny) and Gedomaru regarded him as her first master. And when he died and Billy was banished, Jazzy and Suave put the baby Gedomaru on his hell front door step so he would take responsibility for someone else for once.
It would explain the complicated jabbing and teasing relationship Billy and Gedomaru have, along with how little respect she usually treats him with. But she was also so little that she barely remembers Billy murdering RALRO and therefore doesn’t completely resent him for it.
so yes techinally, Billy really is a Uncle Bill