Hello,
Blueprint merging compatibility will vary from blueprint to blueprint. It’s hard to say what the path of least resistance would be without knowing the specific blueprints. If you could post screenshots of the relevant blueprint code, I would love to investigate further for you.
However, at face value - Copying and pasting the code of the smaller blueprint is good first step, but you have to make sure that the dependencies in it’s home blueprint get copied, too. This includes any blueprint specific variables, references to self, and as you mentioned, references to different blueprint types. If any specific node has compatibility issues, we’ll need to find a workaround or a separate node.