I vote for a long rest too. Jack has only two 1st-level spell slots left, and only 1 sorcery point. Good for a small skirmish but not a major battle. We haven't had a long rest since way back before we climbed Kelvin's Cairn. That was a long time ago.
That said, I'd hope that we can either delay their departure or cause them to stall out along the way.
Jack would be against the idea of harming or poisoning the dogs, unless there's truly no other option. He'd rather try some trickery to cut the dogs loose or somehow separate them from the caravan. If we could somehow get the dogs free of their harnesses, or cause their harnesses to break, maybe for example Jack could cast illusory rabbits for them to chase off in multiple directions.
Disguise self and posing as the half-orc is a good diversion. In combination with that plan, is there some way we could plant some stolen goods on the caravan's sled, so that the town guards would think the entire caravan is involved and not just the half-orc? If they could be detained for questioning even just for one day, we could get a long rest while they sit in jail. Framing them for theivery would be timely too, as it'd be an easy explanation for why they want to make a quick getaway.
We have multiple shape-shifters, right? Maybe it might be possible for, say, Alma to take the form of the half-orc, while Lumrolr takes the form of Torrga? The half-orc could smash a window as a ruse to "distract" a town guard (actually to get their attention) while Jack's mage hand takes some item (a weapon? keys? both?) from the guard, throws it to Lumrolr/Torrga, who runs in the direction of the caravan. The half-orc waylays the guard, who presumably calls for reinforcements. Alma/Half-orc and Lumrolr/Torrga engage in some sort of dialogue with each other where the half-orc shouts something like "meet up at The Blue Clam!" and Lumrolr/Torrga angrily insults him for being an idiot in front of the town guard while she runs off. In the aftermath, if the town guards are able to separate the caravan from their sleds and dogs for a moment, then we try to free the dogs and burn the sleds?
If we could find a rock bar and plant it on the caravan, that could also implicate them in the sabotage. Or, maybe there just so happens to be a rock bar somewhere around the caravan or around The Blue Clam already???