Am I eligible for OCI card ?

I would really appriciate if someone could help me to understand if there is any possibility to get OCI Card for me and my family.

My grandparents were indian citizen but they passed away many years ago. My dad was Indian citizen as well, but he migrated to Nepal and got citizenship of Nepal. I was born in Nepal and based on my Dad's citizenship, I got Nepali Citizenship and Nepali Passport . My dad passed awy few years ago.

I migrated to Canada and received Canadian citizenship. I have already surrendered Nepali citizenship and Passport and thinking of Applying for OCI .

As per OCI eligibility criteria No 4.

-A child or grandchild or great grandchild of a person that meets criteria 1-3 is eligible to apply for OCI .

- The biggest problem for me is to prove "The evidence of self or parents or grandparents or great grandparents being citizens of India at the time of, or at any time after the commencement of the Constitution i.e. 26.01.1950; or being eligible to become citizen of India; belonging to a territory that became part of India after 15.08.1947"

-I dont have my Dad's or grand parents brith certificate. I think their births were never been registered .
-I dont have any legal document showing relation between my grand parents and my Dad.

* My uncle is indian citizen , could he help me in this process ?
* My grand Father's brother is still alive , could he help in this process ?

Thank You
Raju Mishra