Oh, what a shame. Poor rabbits and poor you. I had a similar decision to make some years ago when two of our pups we bred had the same heart defect - one showed obvious signs at 8 weeks, we were told she wouldn't survive the operating table to correct the fault and would die within a month. The other one showed no symptoms at all and at 6 months we found a home for her after having her operated on. She was fit and well after it. But we just let the little one do what she liked when she liked and she lived till she was two! She was far below her normal size and weight but lived a life of Royalty - our lives revolved around Button.
It's always a hard decision to take but I've often heard people say of parents or friends who have gone on in pain and great disability that if they had been an animal they'd have been treated with more respect and given peace.
I'll be thinking of you both.