All couples should have one biological male partner and biological female partner.

List of compatible couples:
>cis man + cis woman
>cis man + trans man
>trans woman + cis woman
>trans man + trans woman

List of incompatible couples:
>cis man + cis man
>cis man + trans woman
>trans man + cis woman
>trans man + trans man
>cis woman + cis woman
>trans woman + trans woman

Anything in the incompatible list is degenerate and should be banned.