Family tree modify

I'm happy about the additional family relationship titles, but, regrettable, it's not possible to modify them in CAS.

I wanted to setting the Spencer Kim Louise family's Vivian and Dennis as in-law to each other, Eric and Dennis as father/son-in-law, Alice and Vivian as mother/daughter-in-law, but I can still only set them as housemates. Is this a bug, or is there a way to correct it?