"What if, in these cases, all concerned are genuinely striving to follow God and they've just reached different conclusions?"
If God has delineated something to be good or evil, then there is no other conclusion to reach than that which He told us.
"Are those in sincere confusion and mistake going to be damned for their lack of understanding?"
I suspect the problem is more willful than accidental for a lot of people.
"As to 1 Cor 6, as I'm sure you know, Paul was writing to a specific place with some specific circumstances and throughout Corinthians, he is addressing some specific concerns they had, offering his advice."
Paul also gave moral imperatives for us to adhere to at all places and at all times. Morality pertains to that which is timeless and transcendent.
"God has not delineated gay folks getting married as good or bad. Literally, that never has happened. Not in the Bible and not to you or me."
The Apostle Paul condemned homosexuality in 1 Corinthians 6:9-10. He says outright that people who practice such a lifestyle will not inherit the Kingdom of God. Paul would have drawn this teaching from the Book of Leviticus which is in the Old Testament.
Are you serious in taking up this kind of a sweeping skepticism toward the moral dimension of the Mosaic Law? What sort of textual critical evidence do you have to support this branding of moral imperatives from God as being nothing other than man-made oral tradition?
"So, if there SEEMS to be some disagreement with Jesus and the OT or Jesus and Paul, we look FIRST to what Jesus said to help us understand the other, not the other way around."
This reasoning would be utterly inexcusable given that both Jesus and Paul held to Old Testament ethics. Jesus Christ upheld traditional marriage as defined by God since the timing of creation: "And He answered and said to them, “Have you not read that He who made them at the beginning ‘made them male and female,’ and said, ‘For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh’?" (Matthew 19:4-5)
"We have Saved by God's Grace gay and lesbian and transgender members, beloved by God. The Bible does not say otherwise. Anywhere. It's just not there."
The consistent pattern of marriage in the Bible from beginning to end is between a man and a woman. It presupposes that kind of a relationship. Never once are two partners of the same gender even hinted at. Never once are more than two genders spoken of.
"But those all appear, on the face of them, to not be any kind of universal condemnation of gay guys getting married..."
But God describes homosexual behavior in Leviticus 18:22 as being an "abomination" and "worthy of death" in Leviticus 20:13. That is indeed a universal condemnation of the practice. Consider this excerpt from the Theological Wordbook of the Old Testament, edited by R. Laird Harris, Gleason L. Archer, and Bruce K. Waltke, on the Hebrew term toeba:
"(heck, lesbians aren't mentioned at all in the OT, so presumably, it's okay for THEM to get married, right?)"
You take liberties by attempting to follow the strict letter of the text in a manner that is favorable toward your own theology. Your efforts to manipulate what it says is disingenuous and proves that you do not really care what Scripture says. How could you possibly be a Christian?
The original audience to whom the Law was given would have understood Leviticus 18:22 to apply to lesbianism in principle. Furthermore, Paul expressly casts such relationships in a negative light in Romans 1:26-27. There is something especially unnatural about two women being together given that they have a motherly instinct.
"I know there are a handful of passages that SEEM to touch on perhaps gay issues, but they are nothing like clear or definitive condemnations of gay folks getting married."
Even if there was only one passage in the entire Bible that implicitly showed God's disapproval of homosexual marriage, that would be enough for a real Christian. That would still count as evidence, but there are multiple lines of evidence showing that homosexuality is incompatible with a biblical theology of marriage.