Renewal of expired passport, need help finding documents!

Hi. My dad and my brother currently both have Slovak passports. I had a passport when I was a child, and was a legitimate citizen, but it expired long ago.

I spoke with the console in my country and they say that I am definitely eligible for a passport, but I will need to start the process all over again by sending over birth certificates... I suppose to prove my connection to my grandpa.

I need help finding the birth certificate of my grandpa, or overall understanding the process of regaining my passport back without the help of a lawyer. I am willing of course to pay for translations of everything, but I just don't know where to start.

Needed to say, I have no contact with my dad or my brother so they can't help.

Thank you!!!