I'm focusing on essential to complement people from different databases. One tricky issue is variance in names like Bob - Robert, Jim - James, Lizzy - Elizabeth etc across databases.

It is possible to research/translation readily available for this type of essential.

Have a look inside my answer (along with the others) here:

http://stackoverflow.com/questions/46007/tools-for-matching-name-address-data/47271#47271

You'd have to implement a research table using the alternate names inside it:

Base      | Alternate
----------------
Robert    | Bob
Elizabeth | Liz 
Elizabeth | Lizzy
Elizabeth | Beth

Then search the database for that base title and all sorts of alternates. You'll finish track of numerous multiple matches that will then have to be checked to ascertain if they match with different comparison of whatever other data you've within the two databases. Maybe the dates from the records in every database might be used - records joined near the coast time indicate exactly the same person.