I never allow nested xrefs in my drawings. I always insert each one individually. This saves me from having to deal with problems like this later on down the road. I can save out my layer states for each file and whenever I get an updated base, it's a snap to swap out.
It may take a little more set up time up front, but the benefits, and the lack of headaches, make the time well worth it.
I would load the two xrefs individually. This will give you full control over each file. You could keep the base xref in the RCP file, just change it's status from attached to overlay