How would I merge 2 characters into one?

How would I go about merging 2 characters? As in, if I have a character in one project that has an inventory system set up and working, and I have a different character on a different project that can build structures and gather resources from vegetation, how would I make both of those characters abilities and merge them? I’ve tried to do this alot with no luck. Every time I will swap out blue prints and follow everything, yet it will still not work for some reason.