Mercedes Sumiza married and had several children: Manuel Carlos (who was a jazz musician), Luis María, Emilia, Haydée, Delia, Adela and Julia.
While his greatest contribution to music was as a composer, Carlos Posadas joined orchestral groupings devoted to operetta and zarzuela at various times in his short career as a violinist, including Penella's orchestra performing in the Teatro Avenida in 1917.
The "Black Posadas" was with other black performers such as Alejandro Vilela, Tiburcio Silbarrio, Rosendo Mendizábal, Harold Phillips and Juan Santa Cruz, one of the regular performers that enlivened so-called "dance schools" and "city cafes", specifically from the dance schools of La Morocha Laura Montserrat and "lo de Hansen".
Carlos Posadas maintained friendships with renowned tango musicians of the era, such as Juan Bergamino (1875–1959), godfather to his son, Charles, whom he had met in Argentina Guitar Association, violinist Ernesto "El Rengo" Zambonini (with whom he used to meet in the café Marathon, of Costa Rica and Canning) and Juan "Pacho" Maglio (with whom he used to meet in Garibotto of Pueyrredón y San Luis, where his friend was playing around 1910).
As a composer he is considered one of the most original authors in the history of tango as a precursor to the current "evolutionary" aesthetic line that later would follow famous performers such as Agustín Bardi, Jose Martínez, Roberto Firpo, Juan de Dios Filiberto and Horacio Salgán.