Palpy got the money through politics, then he got the power through all the scheming he pulled to overthrow the Republic, and once he was in charge, he got the bitches!
Seriously speaking though, Rey being Palpatine's granddaughter is the least objectionable thing here. That was one of the theories being thrown around way back when TFA was released and it could work...if they had continued the story in a way that would have played with the idea of Rey being an Anti-Christ like figure in the eyes of many or some shit.
But no, this is just JJ and Lucasfilm cleaning up Rian Johnson's "They were nobodies!" reveal...and to be (kinda) fair to RJ, they let him do it. If they had a solid plan in place to begin with, they would have told him what it was from the start instead of giving him free range to blow it all up.