I'm an only child, and also the last of my family line. My dad gave me a speech years ago about how I was the last in line, and that it was up to me to carry on the family name. (Also, he asked me if I could name my first daughter after my late grandmother.)
Do I feel guilty for disappointing him? Definitely. But again, there's nothing I could do about it. I didn't ask to have these expectations put on me. And in the end, it's my life, not his.
That's why family members often have such a hard time with transition, is just because they have this big family history built up for you, and they've already written your story in their heads before you've even had a chance to have a say in it. When you're still in diapers, they're already imagining you getting married, having kids, and getting a job, and there's probably a lot of gender cliches wrapped up in that. But I see it as being no different than a parent who's trying to force their kid into the same hobby that they were in, to live out the fantasies that they were never able to. Or forcing them to do something so they can be proud of you doing it. It's ultimately selfish. It's someone else trying to live your life for you.