Complex sentence: Crewe-Milnes' second marriage (1899) was to Margaret, daughter of the 5th Earl of Rosebery and they had a son, also Richard, born in 1911 but who died in 1922.
Split into simpler sentences: Crewe-Milnes' second marriage (1899) was to Margaret, daughter of the 5th Earl of Rosebery. They had a son, also Richard, born in 1911; however, he died in 1922.