He never takes 2 mice after he's done by the first. Now I know that could mean hes not hungry any more, but isnt an adult 20-22 gram mouse every 6-7 days too less for him? Ive tried making the feeding schedule every 5 days but thats been leading to more wasted mice since he doesn't seem to be 'ready' before the 6th day.

As far as the rat pups go, I've warmed them in chicken broth. And scented them with the very same mice he likes.
I think the next thing I'm going to try again is feed him an adult mouse as always and try following it up with a hopper a few minutes later.