Romantic Triad

Ok this one will be short but I have my ruler and her two royal guards. I married my Ruler, Melina and Beatrix, and I realized that the two royal guards, Beatrix and Janet were interested in each other, but also, that Janet was interested in Melina.
So basically it would have been possible to have a lesbian triad between my ruler and her two guards and like, and we can all agree that it needs to happen. So if someone could walk me through the step that would make it possible for a married couple to marry a third person, it would make my day.