Section 4 of application in British Passport...i'm having nightmare fillin it in..i'm done but i'm not sure..

full name, town, country of birth and date of marriage of your mothers or parent 1's parent and your fathers or parent 2's parent..??

what does this meAN??

I have entered both my parents details..yes.. so aside from that my grandparents too both sides?? (mum and dad)....
I havent known them were both deceased when i was a child..or do i need to include them..etc..
am using check and send post office but i need to know wherever i need their information.....i'm having hard time here..pls anyone had inf...