Not sure what you mean with "to the AR" ("AR" is just an outdated term for "advanced relationship", which is just a relationship). If you know who played in which track, you can add a relationship to the appropriate recordings. If you only have general information, add it to the release (relevant guideline). I think @jesus2099 might have some script to make it easy to copy the relationships to the other versions of the release if you add them at the release level, not sure.
They should be merged if they're the same physical product sold in two markets. If they're different in any way (different barcodes, different legal texts, anything) then they're two releases and shouldn't be merged.