Hey y'all, is there any limitation on how large an object a tractor beam can grab? Or could a group of PCs in a YT-1300 hold a Star Destroyer with a light tractor beam?

The easiest way to rule is that when two ships are in tractor lock, they maintain position relative to one another unless the operator of the tractor beam opts to "reel in" the beam. As far as the pair moving relative to objects outside the tractor lock, only the larger vessel (by Silhouette) can move the pair.

This means a light freighter can tractor a Star Destroyer, but the SD dictates the movement of the pair. The freighter can use the tractor beam to decrease the distance between them if it likes.