FLR - Marriage certs of parents & grandparents??

Hi

I posted a couple of weeks ago about obtaining my full birth certificate which I have done. I now have certified originals of mine, my father and my grandmother. This is for an Ancestry Visa extension (LTR).

However I have noticed that the home office also mention submission of marriage certificates of the parent and grandparent in question. Is this really necessary? Will I get rejected if I don't submit this?
I imagine I'll be able to source my parents marriage certificate but my grandparents? - no chance, I would have to apply for a new one. They have both passed away and what's more they are from a state in which my direct family do not live so getting the wheels in motion could be challenging. I live in London and my family are in Australia.

Can anyone else please comment on the necessity of said marriage certificates? I'm slightly paranoid the home office will reject anyone that doesn't tick their boxes.

Please continue in your previous topic.