I've beaten him with every weapon now except for the bow. I need to power up the bow, because I haven't spent any of my titan blood on it yet (it's my least favorite weapon). I almost got him with the bow when I really powered up my special, but Hades got me before I could get him the whole way down.
As far as the companions, I finally killed Skelly and got his companion, but I haven't been able to get anyone else's yet. I want Achilles', but even after I spoke with Patreclus and returned to talk to Achilles, he still hasn't given me the companion. I also can't seem to give him any more nectar's. Also, I don't know what people on here are talking about but you CAN NOT give Thanatos any nectars. I've only seen him in the palace once, and every time I see him on a run, I can't give him shit. He shows up, kills a bunch of stuff, says "you didn't see me" and disappears. I don't know if it's because I have the Switch version of the game or not, but he absolutely will not take any nectars from me. Same with the Minotaur. I saw Meg in my bedroom, but haven't been able to give her a nectar since. I don't know if I missed my chance to get her companion or not. That's the only part of the game that's getting really frustrating for me.