Remove or lock feature allowing multiple memberships at once

Currently a person can be assigned both a family and individual membership at the same time.  Someone must want this feature, but for our facility it is causing issues.  Human Error, members are being given multiple memberships without an error message from CR causing members to be charge incorrectly.

I would like way to remove this option ( ie only one membership can be assigned to a person at a time) or CR provide an Error message (something like.. are you sure you want to assign this person two different memberships simultaneously) when an admin or sub-admin is using the system.

Thanks!