For Lupin I'm tossing up between:
1.
and
2.
1. Yes I know, I said that I didn't want grey petpets, but I meant that I didn't want grey with silver

. I think these 2 match really well, and the petpet even fits in with how lonely and withdrawn he would have been during those many years without padfoot and prongs

I was also concerned that any grey suggestions would look TOO gloomy (which wasn't the look that I was after) however I think that in this case, it fits him. The calm, serious (and somewhat sad) figure also contrasts with the neopet which still looks youthfully-active, energetic and even a little fierce.
2. I also love this match because again, not only do the colours match, but I think they work personality wise. Doglefoxes (who like finding treats for their pets) are very loyal (like I imagine lupin) and i imagine, intelligent, which fits in with his studious personality. Even the fact that he's a rugged-looking mutant/werewolf hasn't taken away his charming personality.
I'm tossing up between these 2 pairings atm, but I'm still open to other suggestions.