I'm totally not up on the mission of the ACLU, but from what little I do know, wouldn't this be something right up their alley? C'mon! American Civil Liberties!!!!
So the Mormon church isn't part of this. The people getting sued are the people who either represent (third parties) the Mormons or allowed the Mormons to influence them.
On a different less exciting note. This will fail miserably because a voter approved law isn't the same as a constitutional amendment. The legislature is well within their right to change the law however they want. The same as any law that is on the books.
And please remember that it isn't against the law to lobby someone or something it is potentially against the law to provide goods, services, money, quid pro quo, and the like. Since Mormonism doesn't offer anything tangible, because face it eternal life giving Elohim a blowjob is a wish and fantasy, Mormons and their people haven't done anything legally wrong.
Lastly and leastly, when was the last time Rocky won something like this?