Law / I am half Polish person who would like to have Polish passport. My grandfather's family lived in Warsaw. [4]

Hello, I am 22 years, I live in israel and I would like to have polish passport.
I am doing this process with a lawyer in tel aviv.

But there are some difficults things with my case.
My grandfather's family lived in warsaw and I am not sure if it is possible to find any documents. as for now.
I don't have any documents.
What do you think I should do so I can have my polish passport? any advices?
Soon I'll visit Warsaw to meet with a lawyer... So I want to get any advises about my case which is little complicated.

These details I have:
1) Mordechaj Yederman (Jederman?) - Father of the grandfather.
2) Malka Yederman (Jederman?) - Mother of the grandfather. Died in ghetto warsaw.
3) Israel Yederman (Jederman?) - Brother of the grandfather. Died in ghetto warsaw.
4) Gabriel Yederman (Jederman?) - Only yesterday I discovered that he changed his name in israel.
5) Gabriel Yederman (Jederman?) - Was born at 1922/15/5. (or 1922)
6) Gabriel left poland (warsaw) at the date of 1937.
*Note: only yesterday I discovered that my grandfather (Gabriel) had another name in poland, In israel he changed his name to "Gabriel", but I don't know what was his name in poland (warsaw).

To conclusion, I have enough information to do something with my polish passport? What can I do so I can have polish passport?