Who is Demon Veen from Ada; or, Ardor: A Family Chronicle and what is their importance?

Demon Veen is married to Aqua. Veen and Aqua have one son, Van. Veen, however, father's another child with his cousin's wife..... that child is Ada. Demon Veen is described as a wealthy man, who travels extensively. He is killed in a plane crash in 1905.