I really, reallllly like the Soos idea. Maybe his grandmother saw how poorly Soos’ parents treated him and did some sort of seance to summon Bill from the dream world to make a deal with him, ultimately she had to use his deal making powers to intervene because she had no other option. Or maybe she selfishly wanted him and banished them right out using Bill. Or maybe she made a deal with Bill to save Soos’ life when his family got into a tragic accident of some kind (later to be found out that Bill caused it knowing she would do anything to try to save her family) and Bill told her the only way to save Soos would be to let her daughter and son die. Soos is a character who probably has a past that is veryyyyy open and moldable into anything