@Royday According to Unreals licenses, you should definitely be able to share within a team/organization, for organization. I believe it really depends on each asset specifically, just because the creator retains their Intellectual Property Rights.
I believe most assets are able to be used in shipped games/projects, the only ones that are specifically mentioned to be excluded are:
“Without Epic’s written permission, Marketplace products created by Epic for an Epic game may not be used to create sequels or recreate, emulate, or republish those games.”
So it seems as long as it’s not Epic’s Assets to be used to re-create their games, it is okay.
But, I’d also have your friend help make the games as a precaution.
I hope this helps, and let me know if you have more questions!
-Zen