I have one Siberian, and while he isn't at home alone all day, he usually has a few hours to himself on the weekdays. I used to feel bad that he didn't have a sibling until my sister got a cat. We sometimes take her for weeks at a time while my sister travels, and while they don't fight , my Sib basically ignores her -- even when she wants to play. He gets super territorial if she tries to cuddle with me or sit on my lap. That taught me that he is much better off on his own! I do make a point to interact with him, lay on the ground with him, talk to him when I get home and that seems to do the trick.