Foreign birth registration

Yes. I recently did this for my kids and had to put my docs in as well as their grandma's..

We got a solicitor friend to do it but you can ask drs or solicitor firms (for a fee).

Hi, I did this for my daughter. She has two Irish born grandparents via me and dh. However, we chose to use my Mum's details for the rather ghoulish reason that Mum has passed away and there is a death certificate for her. My FIL is very much alive and we would have needed to find a fair bit of documentary ID for him. Which he doesn't really have.
Although, I still had to find documentary ID for my Mum and for me because we had both name changed when getting married. I also need my own grandmother's maiden name because that was on my mother's birth certificate.
The Live chat function with the passport office was actually very good and responsive. As was the "this is what you need to give us" list provided.
The easiest route would have been via a male parent and grandparent because there is less likely to be a name change.

Witnesses? We just used a local notary. It was worth it. My nephews used a solicitor friend but we don't have one handy