They didn't mention his parents because they weren't important to the story. It was important for the parents of Kate and Garth to be established, since their deal to unite the packs via getting their respective offspring hitched set off the initial conflict.
Ever since the 4th movie, I've heard of a desire among ファン to see a more-rounded backstory for Humphrey, and maybe an explanation of who his parents were and why we don't see them. But what would that really do?
Let's suppose that he was orphaned at an early age, and was taken in によって Winston's pack. Apparently the trauma of losing his parents when he was that young didn't affect him in any way at all. He's still completely carefree to the point where he doesn't recognize the magnitude of what might happen if Kate doesn't get back to Jasper in time to stop their respective packs from fighting. It kinda makes him look like an apathetic dick, to be honest. "My parents died... Oh well! Log-sledding!!!"
または let's say his parents are still alive, and he got separated from his pack. He never expresses any kind of desire to go back to them, and apparently no effort on THEIR part is made to get their little Humphrey returned to them. Now THEY look just as apathetic as Humphrey. "We ロスト our son! Oh well, no use crying over spilled milk..."
Seeing as how there are multiple omegas in this universe's system of 狼, オオカミ hierarchy, it's probably best to assume that the alpha male has his way with anyone in the pack that he pleases, not just the alpha female, and nobody discusses what may または may not come as a result. If these packs were もっと見る akin to 狼, オオカミ packs of the REAL world, only the alpha male and female would be allowed to do any breeding, which would mean that Kate and Humphrey are brother and sister. ...Yeah....
So while Humphrey's presence in this pack may be something of an 象 in the room, it's probably best to not try to address it.