It depends on how WoW set up the game. In the MafiaScum page they say the mafia should pick a member between the three and that's the one that goes out to perform the kill, and that's the one that has to be roleblocked (and technically, the one that would be killed by the Paranoid Gun Owner)
But we've never played with those rules, at least not in the round where I was game mod (I haven't been mafia yet). So, if there are two and we roleblock one, I don't know if WoW has been asking for them to pick a killer, if she'll choose randomly to know if the goon's blocked, or if she'll roleblock all the mafia altogether.
As for the Godfather, he's the one that PMs the kill, that is the one who decides it, but then again, in that PM it should say who's supposed to perform the kill, dunno what would be the case here