Quoting Mrs.O!:" wolf hybrids are no joke, they may be smaller but they still have wolf like tendencies..SHE has to be ... [snip!] ... submissive in order for him to get a long with other dogs...is he neutered? if not I'd get him snipped as soon as possible..."
"wolf hybrids are no joke"
We have big dogs we have a Pit bull and a Rottweiler pit mix and a Cane Corso and they are all big dogs. But I feel that Wolf mixes are not "dogs" they are Wolfs! That is something important to keep in mind, they have not been domesticated like other dogs.
They need to have a VERY strong pack leader who really understands pack leadership, otherwise things can go down hill very fast.
Any way to answer your question Bear is trying to establish dominance over your dogs, the humping is a very clear sign of that. I don't know how much you know about dogs and pack mentality but please remember that his is not just a "big dog" it is part "wolf" and they need to be trained by someone who does have a clear understanding of these things.
If you or your sister can not handle training it properly then it is her responsibility to hire someone and make sure the Wolf is properly trained and socialized.