A bisexual marriage includes a minimum of 3. You are correct.
A person who does both male and female must have both a male and a female. Otherwise, we’re discriminating against the “poor dear”.
Besides, our Islamic cohorts require the US to permit polygamy for them to practice their religion. They might be underwriting some of this social change, too.
The mere existence of “bisexual” people underscores the fact that homosexuality is not an inherent unchangeable characteristic, but instead underscores that homosexuality is a “PREFERENCE” which indicates that the person is engaged in a conscious CHOICE as to whether or not to be homosexual, bisexual, or just plain promiscuous.
Just because someone is “oriented” towards a behavior does not mean they are compelled by their nature to engage in that behavior.
You could just as easily say that robbers and thieves are oriented towards covetousness and that we should therefore tolerate and embrace their lifestyle by legalizing theft and robbery.