This is a tough one, and there's no magic answer. The reasons for rejection are varied. It may just be that the publishers feel there's no interest in intergenerational, autobiographically based novels this year, or this decade. That doesn't mean they are right, but they are the ones who make the decisions and there's not much we can do about it. Unless you are willing to try a different kind of novel, there's not much I can suggest.
Writers live with rejection.
I had one last month myself. My first children's book was turned down 25 times. It sold on the 26th submission. People say to me, well, rotten books get published all the time. Or maybe they are just rotten in that person's opinion.