Oliver, I don't know about your relations with your parents, but I think they might be of a similar age as I. We grew up not knowing about any of that whole transgender stuff. In fact, I had no clue what was going on with me, I just knew that I was different than my peers, and different was mostly considered to be a negative thing!
Here are your parents sitting, not only having one child who is different, but two of them! They might wonder, where they went wrong in raising you kids, after all, they did as good as they knew, and they feel guilty that they failed!
Would it help if a therapist would talk to them, explaining that it is not their fault that you kids are how you are? Would they understand that it was a hormonal imbalance in the body of your mother while you were in the early stages of development, and that his is nobody's fault, but just the way mother nature decided to play the game?
Most parents hope to have grandchildren one day, and dream about how wonderful it will be to spoil them rotten, and once they are spoiled, send them back to their parents (it is payback time

). And here are your parents, who have all those dreams shattered, because it is likely that none of their kids will have children. I am in a very similar situation, my son is as cis as they come, but he and his partner don't want to have kids, no matter what the reason, the result is the same.
My kids appeased me telling me that they can always adopt kids, if they feel like having some. This is an OK compromise for me. Would that help with your parents?
Please try to understand your parents, and try to talk with them on an adult level, without any of that blaming stuff, and hurt feelings.
My parents are gone since long, but I still miss them quite often, and I wish they could see me as a proud woman. Most parents don't want to have a bad relation with their kids, because why would they, after all, they love them. Try to understand each other, and try to leave any egos outside the room! They will not live forever, and once they are gone you will miss them as much as I miss my parents!
Hugs
Linde