coguardian
/kɒɡˈwɑːrdɪən/Definitions
1. noun
A person or organization that shares with another the responsibility of caring for or managing something.
“The hospital had two coguardians for her care, her parents and her grandmother.”
2. noun
A person or organization that shares with another the responsibility of administering a trust or estate.
“The coguardians worked together to manage the inheritance of the deceased.”