I am in this position and have been for over 25 yrs. I found out that my mother died by finding a notice in the paper and was contacted by a solicitor to say that my father had died.
I have my own teenage children, married and to the outside world have a nice life. I have spent a lot of time with my husband's family over the years.
I feel that you are never "normal", you are not like other people due to your experiences growing up and the lack of normal talk of family, siblings with children etc etc. I have siblings who became mentally ill before I had even left home and they have never worked and never married. I tell people that I am an only child.
I would be interested to hear from someone in a similar situation.