Well, thanks to this chart here made by @torchmlp, we know that Sam and Dean weight a little less than three crayons each if we compare them at 1/19th of Jacob’s size.
Jacob lifted weights in school, and has a stronger build than either brother. People have clung to buildings with their fingertips holding up their weight before, when their life depends on it, so with one finger, if Jacob can get all the regular-sized guys in the lounge to fit on one, he can likely lift all of them. Throw in the smols and Rumsfeld and Bobby, he’s still not going to have a problem.
Jacob would probably run out of room for more people before he started to feel too much strain of their weight. Then they’d have a giant who was worried about them all tumbling off the side, so the little guys had better be in pockets for this experiment. Jacob would be so amused by all these little guys trying to test out his strength.
I can almost imagine Sherlock being torn between helping to add weight and wanting to write all this down.
Brothers Apart 