mmm... not sure exactly what Mamange is, but I wonder if Utsuho and Rin would still be "pets", or if they'd be "orphans" who are adopted into the Komeji household.
Yuugi doesn't really have much relation to the Komejis, although seeing her as a mother figure would practically be as bad as Yukari as a mother when illustrated by Shino. ("What? Don't tell me you're full, you've hardly even touched your booze!")
I guess Kanako or Sanae or maybe even suprise-I'm-reverting-to-adulthood-and-showing-you-I'm-a-better-mother-than-you-both-combined Suwako would be the ones who most would have reason to take care of the... although Marisa seems to have done a decent job in the series this artist did on the subject.
Ah, then if it's about servants, Rin would be the one who would be most appropriate.
If Rin has to stay childlike, though, I don't think any of the underground youkai would take in the Komejis, though, since none of them seem to particularly like the Komeji family... (Although mama Yamame - Mamame? - would be funny)
I have to think it would get tossed off on a frazzled Sanae, who might have to care for child versions of Kanako and Suwako at the same time...