Brenna married Maria Trauenfeld, whose father was employed by Frederick Eugene, father of empress Maria. Exact date of the marriage is unknown; it probably took place soon after Brenna's arrival in Russia. They had a daughter, who was around sixteen in 1798, and whose later life remains unknown (her name did not appear on the immigration records when Brennas left). The Brennas maintained modest lifestyle in Pavlovsk and Gatchina until Brenna relocated to Saint Petersburg in 1796. In 1798 they moved to former Trauenfeld residence; Brenna purchased this building one month prior to Paul's murder.