Let’s not complicate things here. Would you do the same with a legacy bank account? I don’t think they allow 2 names on a personal account. There’s a difference between legal name and common name, if a person officially change their name due to marriage then her/his birth name becomes common name. If that grandma keeps sending cheques in her assumed married name she needs to remind her grandma not everyone changes their name after marriage.
I received cheque in my name only and deposit it into a joint account no problem, haven’t seen any cheque for 2 recipients.