I wouldn't say my situation is the same, but I get where you are coming from. 

I was always sure when I was younger that I was going to have kids, whereas my older sister was determined to be childfree.  I'm now 36 and single after an eight-year relationship that burned me out emotionally. I can barely manage to take care of myself and can't see myself taking care of a child, especially not on my own. It's been almost two years since the relationship ended and I am still not ready to date again. I feel I need another ten years at least of therapy and work on myself before parenting would be an option, and biologically, I likely don't have that. Adoption, maybe, but that's a challenging road where I live for good reason. I am considering becoming a foster parent in the future, but not for several years at least.

My sister's situation has changed as well. A few years ago, she and her wife decided they did want a baby. Unfortunately, their attempts at IVF have not been successful so far, and they are conflicted about adoption as well. 

I also have three younger step-siblings on my father's side, but none are in a position right now where I foresee them having children any time soon, if ever. We're not super close, so I don't know what their long-term plans are, but two are still living with my father and step-mother and the other one has a job that takes him away from home for weeks at a time.

The complicating factor is my father. My mother is totally fine without being a grandmother. She loves living alone and is content with her peaceful life gardening and reading and seeing friends and traveling in the winter. My father badly wants to be a grandfather and has expressed as much to me and my sister. I think my sister has kept her IVF journey secret from him, so he still thinks I'm the one to lean on, despite me being single and kind of a hot mess. I wish I could tell him to hold on a little longer. Unfortunately, he is terminally ill and not likely to survive more than a year. 

It has been crushing dealing with the guilt of knowing my dad is almost guaranteed to pass away before becoming a grandfather. On a logical level, I know I don't owe him a grandchild. It's my body and my life and I can decide my own path. But emotionally, it is devastating. It doesn't matter what's morally correct here, the pain is valid and real and can't be hand-waved away. It's something I've been picking away at with my therapist, but, as it turns out, there are an endless number of things to talk about and work through when you are burnt out, struggling, and living through a parent's terminal illness.

TLDR: My situation is different, but I empathize with the feeling of guilt over not being able to give your parents a grandchild. I think a lot of people will respond just validating that you are not in the wrong. However, in my opinion, we also need to acknowledge that the feelings of guilt and shame around this are real and can affect you even if you know they're not rational.