Before I respond, let me just say that I think reasonable minds can differ on how God views gay marriage and gay sex within a gay marriage. I obviously feel good about my position, and you yours. And who is "right" I think is not that important. I enjoy the discussion.

"THE FIRST COMMANDMENT that God gave to Adam and Eve pertained to their potential for parenthood as husband and wife. We declare that God’s commandment for His children to multiply and replenish the earth remains in force. We further declare that God has commanded that the sacred powers of procreation are to be employed only between man and woman, lawfully wedded as husband and wife."

Yes, that is potentially problematic if we accept "the powers of procreation" to mean sex between gays. Although, there is an argument to be made that gays can't procreate, so they are not engaged in "the powers of procreation." It's a creative interpretation, admittedly. On the other hand, perhaps the choice of words was inspired to allow for that distinction. After all, they could have just said "sexual relations" or "sex" or "intimate relations" or whatever, but those wouldn't have allowed for the distinction.

"So the 15 "Church leaders" that signed the Family Proclamation are wrong? These aren't just random church leaders either."

Yes, I think it is entirely possible that they were too influenced by the cultural and societal norms of their old-time generation(s). Church leaders make mistakes all the time.