Membership Renewals with 'Partner' relationship causing membership lapses/missing contribution
"Ultimately what we want is either Contact A or B to be able to renew the 'joint' membership - does Civi support this?" No it doesn't support this. Generally I think users work on assumption that reminders should only go to Contact A, andI would suggest preferably with a checksum to a renewal form that sets First/Last as read only to stop contact B clicking on the link in the email without checking who it was to, and hence avoid risk of having name overwritten