Combine worlds and character

Thank you so much for the quick response. I got a follow up question. What if the worlds and character was created by different teams that is not in association with our team, we do have the source code of these worlds and characters. Can we still combine these worlds and characters if they were all created by unreal? What if these were all created by different engines, like by unreal and unity, can we still use unreal to combine all these?