Validate relationships

I have a numeric roster which I use to rotate through the members of the household. I would like to validate that when person A states that they are the partner of person B, that person B must also state that they are the partner of person A.
I cannot use a list question as we do not ask for names of the members of the household for anonymity, therefor my only option is numeric based on household size. As the source question I am linking to their birth date.

Ideally I would like this as a filter as this will be an online survey and I want to avoid mistakes. What is the best syntax?

Two twin brothers, for example born on 1970-01-01, one of them is married. Which category “1970-01-01” or “1970-01-01” do you select in the list when you interview the spouse?

See validation 3 for spouse_pid_1 in the “Household Roster” public questionnaire (Public Questionnaires tab > Standard modules > Household Roster > section “B-2 …” > spouse_pid_1)

Here is the direct link.