I am preparing everything needed to apply for my first British passport. While reviewing the required documents, I see that I must submit all uncancelled previous passports. Since I have been in the UK, I have had three passports. Two of them have expired, and although I still have them, the government cut the corners when issuing my new one. The third passport was lost, and I had obtained a replacement like a year ago.
1) Would these two corner-cut passports and my current passport be acceptable? Thy don’t have any cancelled stamp.
2) I am required to provide the email address of someone who can confirm my identity. Can this be one of the referees I listed in my application, or must it be a different person?
3)regarding my parents’ marital status: my parents are elderly and married (I think so

4) Lastly, do you recommmend passaport check and send service by post office? Is this increasing the speed of the process?
5) any other recommendations are appreciated
Thank you for your help.