[LunarBerry]

I'm currently going through this sort of thing. I have two older Jack Russells (one a little over 12 and the other about 6-7, both are a little hefty in weight). I had gotten my baby yorkie last week and at first she seemed to want to play and the other two would just back away from her, not knowing what to do or just didn't want her to bother them. My oldest girl seem to show more interest and right now she has gotten to where she'll check on her and occasionally play with her (and sometimes doesn't want to be bothered lol) the other girl doesn't seem interested in her at all currently, though I'm hoping that'll change. So yea personality is a big thing. I was counting on the older one to kick in her maternal instinct & help teach her and she has (though she's fixed and never had a pup, let alone really seen one but has show strong interest before in mothering). Sometimes they may surprise you, but it's important to bring them together a bit slowly and watch how they react to see when it's alright to let them be around together.