Thank you so very much for your input on my question, but of course I still welcome any additional viewpoints from the community.
I am persuaded for now that the best approach with my kids in my situation is probably to start by slowly, over time, probing their opinions on the "LGB" topic as that is more visible in mainstream tv, movies, music etc. and they have met some of our LGB friends. Then I think we can slowly add "T" into the discussion before ripping the band aid fully off.
I have decided, however, to withhold disclosing to the kids until after we cross the bridge with all of our adult family, some down, many to go. I am so blessed that my wife is on my side ... for now ... But I also have always lived by the philosophy that there are no guarantees in life.