I'm surprisded your son and his partner need convincing. I'd be curious to understand why they wouldn't want to move. Is it a lack of places to go to?
It's a real dilemma, I recently read about trans people claiming asylum in Europe but being denied because the US are still considered a safe country. Which is not true for all of the US anymore.
I hope you have a safe trip!
Oklahoma really isn't any better from what I could find on wiki. Cities big enough to have a zoo should hopefully provide a few safe spaces for LGBTQ+ people.
I wish you and your family well.