The brothers-in-law referred to in the header to responsa 10 are the the "Shoel Umaishiv", Rabbi Yossef Shaul Natansohn, and his brother-in-law, Rabbi Mordechai Zev Ettinger, author of Shut Maamar Mordechai. The two studied together for many years and authored several books together, most notably the "Mefarshai Hayam" glosses on the "Yam Hatalmud" on Bava Kamma by their uncle, and Magen Giborim on Shilchan Aruch O.C. They were NOT brothers-in-law of the Chasam Sofer.