How do I combine 2 separate Apple IDs and all the iTune/iCloud purchases/data/access under one Apple ID, preferably my current one?

How do I combine everything from my deceased husband's one or more Apple IDs into my own 1 Apple ID ( preferablymy current Apple ID)? I want to maintain it all under 1 Apple ID; the data and access includes iTunes/Apps store purchases and major OS upgrade purchases, iCloud access and storage, and multiple email addresses. (I want to be able to reflect these references to his previous email addresses in my own Apple ID, if at all possible!). Going back and forth between 2 different login/accesses on the same MacBook Pro is frustrating and confusing.

[I also need to do the same with all access to his files that he created and that are maintained on the hard drive and back up; Any suggestions are welcomed! ]

😕Could someone let me know if this is possible and if so, how best to initiate this migration?