The brothers – To keep it interesting, I’d say Sam ends up swapping into Jacob, and Dean into Sam! That makes Jacob the shortest of the group, and poor Sam, who has the least experience being full-sized, finds himself too tall! He might not even get as far as discovering how strong he is now considering how nervous he’d be around the two really tiny guys. While Dean’s just complaining about how long Sam’s hair is and it gets in his eyes and how can you deal with this Sam.
Jacob – Jacob would be super weirded out to see how big everything is. He’d also have to concede that, yes, he very much does seem to stomp around and cause earthquakes. He’d have to hope the Sam-swapped-Dean was able to get over the shock enough to look after him, because he doesn’t have the skills like the brothers do for surviving that smol!