Hi Johann and Laurent,
Thank you so much for this information. I do think my ggg-grandfather Schia Landau and Salomon (Salo) Landau were brothers. Schia Landau was also born in Nowy Sacz (~1841) and his father was Judah Leib HaLevi Landau. Interestingly, Sophie Wachmann's sister Amalie Wachsmann married Schia's nephew Josef Baruch Landau, which further strengthens the connection to my family.
Thank you again!