There is nothing to allow.
The concept is incoherent.
So-called gay marriages exist on paper only.
Marriage is about procreation. It’s an agreement between the man and the woman to commit to having and raising children.
Yes—old people get ‘married.’ But they are just larping, like Civil War re-enactors.
The same holds of same sex marriages.
Yes, same sex couples can adopt.
And maybe that works, a little bit, sometimes.
But, singularities aside, adoption only works when the child is being absorbed into a pre-existing biological family or when the child is being transferred from parent to uncle or grandparent or some such.
When the child is adopted into some alien household, the result—and therefore the purpose—tends to be molestation or trafficking.
Which is suggestive in the context of this discussion.