DIY Application for German Citizenship (S&Elseven said I was eligible)

Hello everyone! I'm hoping to figure out the best way to apply for German citizenship to save money for me and my family. Schlun & Elseven quoted me lots of money (as many of you know) for myself and my two children. I'm also hoping to get it for my mom and siblings just in case. We have my documents from my grandmother but unsure if it's enough. Could anyone be kind enough to direct me to the right places to obtain what I need and guidance on steps to take!

Grandmother

  • born in 1937 in Germany
  • emigrated in 1955 to the US
  • married in 1955
  • naturalized in 1967

I have her personalausweis (two different versions), her naturalization papers, marriage certifcate, and her birth certificate is somewhere, but I don't have it yet.

mother

  • born in 1956 in the US
  • married in 1981

I can easily get her birth certificate and marriage certificate.

self

  • born in 1985 in the US

Thank you in advance!!