Since I'm not young, nor a man, nor a member of any church I can't answer a question clearly not addressed to me.
I do not think they would have a problem with the church keeping the term marriage if it meant the government afforded the same rights and tax advantages as a male/female couple.
But the Government, that is Congress changed the tax law to expressly promote the institution of Marriage by giving them the tax advantages. Right or wrong, that is what happen. It seems the answer is to lobby Congress to correct the blunder not change the meaning of Marriage so that the reason the tax advantage in the code, no longer isolates the intended targets.
Well yeah! Simply bitching to the court about the grievance using the 14th amendments equal protection is convoluted and disingenuous to say nothing about probably incorrect.