If an ally is jammed by a huge ship and Yorr attempts to intercept the stress, does it "work"? or does the wording of jam make it so that Yorr takes two stresses then the huge ship keeps jamming the ally to two stresses also?

You can pull as many stress with Yorr as you want, up to his limit, but the Jam target is still going to end up with 2 stress. You wouldn't actually have to max Yorr though, you could theoretically pull one and then let the other two go through. Can't think of any reason to do that off the top of my head, but who knows what the future may bring? Keyen opened the door to ships being able to benefit from stress, there may be another mod or crew that would make a free stress for Yorr a good thing.

But for now, I have no idea why you'd do it, but you can do it.