Don't take this the wrong way, it's not meant to be a criticism. But I would work on teaching the kids (and I know it's hard with a two year old), to not lay on top of Harry for one.
It could very well be the 'new addition',,I know when I had two males who never ever ever once got into a tiff, DID, when I brought in a new puppy..Granted these weren't kids they were directing to, but dynamics change ..
The bully stick, well that's a really HIGH value treat, I see you have a good plan for the next time, (crate him if he has one)..
I'd kick his butt off the bed, (not literally you know what Imean
, he may be getting a little to 'possessive' of things like the bed/couch..
Certainly no expert here, but yes I'd rule out medical, maybe he's sore from something, but I wouldn't say that was the case with the bullystick..
Hoping others will chime in, good luck to you and welcome to the forum