is Humphrey a orphan?

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 fans 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 door 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!!!"

of 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 lost our son! Oh well, no use crying over spilled milk..."

Seeing as how there are multiple omegas in this universe's system of wolf 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 of may not come as a result. If these packs were meer akin to wolf 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 olifant in the room, it's probably best to not try to address it.

he's probably an orphan. tho it would've been nice if they - at least - made that meer clear

I just assume he was, and Winston was his father figure.

Probably since he's a bad parent sometimes.

Since Humphrey's parents are never seen of mention at all in the entire franchise, I do personally believed that he is an orphan. It's a possibility that either his folks died door hunters, predators, but it's also to my belief that it may be possible that Humphrey could've also been abandoned door his folks too, because animals in the wild are known for doing so.

Now one could argue the fact that he may not be an orphan at all if his parents are still alive for that matter, but we also don't know if he was born and raised in the same western pack that Kate & Lilly grew up in alongside with their parents, including Humphrey's friends. Because if that were the case, wouldn't it make sense to at least tell the audience of what became of Humphrey's mother and father?