Toruu
As long as they have Molly's support, that's good, an adult on their side can help a lot. Especially since if someone from the ministry comes and sees several minors doing magic without parental consent, it can cause problems for them, like much a fine or something like that, that is, all the work would be lost. On second thought, he could save Luna's mother, who was a potions and magic researcher, a possible teacher, who the hell could play the game and replace Snape. What's more, in exchange he can ask Luna's father than in the newspaper name your store, it can give them some publicity, haber is not as big as the Prophet but it is certainly useful. Also having Luna's father on his side would be helpful, he could announce Peter to the world, and the Ministry could no longer sweep him under the rug. A threat to Ron and his family, let alone him.
Molly not being able to use intermediate magic? Didn’t she duel and win against Bellatrix?( been a while since I read it) None of the Weasley’s have been seen haveing lacking power… Cursebreaker, Dragon Controler…(dragon raiser Idk) Ronald is the only welp of the group and that seems by pure laziness. She and her husband are in the O.O.T.P. I assume their not near squibs.