I'll admit I haven't read the rest of this thread, so apologies if these are already posted (both marriage related).
Opinion 1:
The government should not have anything to do with marriage. The gov't could setup civil unions that grant the same legal benefits to any two (or more?) persons, but marriage itself should be the purvey of the church and the gov't has no business being involved in it.
Opinion 2:
Polygomy should be legal to any group of consenting adults that want to have the legal protections of what we currently call marriage (see opinion 1). So if opinion 1 was law, any group of people who want to enter into a civil union granting legal benefits to each other should be able to do so.