So, the first male Hortons (who bear the name of Horton) appear to be Evan Valkyrius (born 2068) and Jaden (born 2073).

Though, E.V. has the Celestial Taint, and Jaden is Untainted, so we still have no male Hortons with a normal Taint (like Serenity) within the canon...

Sasame and Danica Horton both have daughters, but I dunno about their children just yet. So, the above might still change.

Alas, Georgia Horton Sr. (Valkyrie and Xydia's sister) died before she could have kids...