Bart Cary is a doctor and an adventurer who moved to Bangalla to start a jungle hospital which the 19th Phantom funded when he saved his life. His younger sister ended up marrying the 19th Phantom. After the hospital burned to the ground he traveled around.
It is assumed the Cary family had some money originally. It is assumed that Barts and Janes parents have died before they meet the Phantom as Bart was asked permission for Janes hand in marriage.
One of the places he stayed and worked in was Bolivia before the second world war. He eventually moved to the USA and married and had at least three children including two boys and a girl who was the youngest. His family has money and was built on hard work and the luck from the good mark of the Phantom.