There are many valid points for both allowing and disallowing same sex marriage.
On one hand, PlaneShift should be an escape and so, allowing same-sex marriage would help a lot of people do that.
On the other hand, PlaneShift has to have it's own world that fits closely with cultures in similar time periods, disallowing same-sex marriage is the best way to do that.
Now, whether Laanx and Talad even care about it in another point. We can't compare them with the gods of our world.
But, one must note that Yliakum isn't the most peaceful of places, children are trained to fight from a very young age. I imagine many people would die every year and in order to keep the population growing same-sex marriages would be disallowed.
This can go either way and is completely up to Talad and Xillix to decide.
Worst come to worst, one male partner can play a female or they can both play Kran.