sorry for your loss but something should have been done with their ending capital accounts. don't know what the partnership agreement says about death of a partner. that's the first place to look. but I wouldn't be surprised if there was no such agreement. with no agreement, if they died intestate (no will) the state's laws would dictate what happens to their interest. If they had a will that would dictate. if held in their "living" trusts that would dictate. you may need to see a lawyer because that 2021 return may be incorrect. they can review the documentation and indicate how to proceed.
in short, someone(s) inherits their interest. certain adjustments made need to have been made.
