Would you elaborate on the following sentence structure and grammar. It seems somewhat complex. What is the function of "becoming prosperous" in the sentence? Is it a reduced form (if yes, for what?)? In the case that it shows contrast, why has the author used and as a conjunction?
They succeeded, becoming prosperous, and piety mingled with smugness made the whole family insufferably sententious.
The context of this sentence is a paragraph from Paul Theroux's article in the Smithsonian magazine, "The Trouble with Autobiography":
My maternal grandparents, Alessandro and Angelina Dittami, were relative newcomers to America, having emigrated separately from Italy around 1900. An Italian might recognize Dittami (“Tell me”) as an orphan’s name. Though he abominated any mention of it, my grandfather was a foundling in Ferrara. As a young man, he got to know who his parents were—a well-known senator and his housemaid. After a turbulent upbringing in foster homes, and an operatic incident (he threatened to kill the senator), Alessandro fled to America and met and married my grandmother in New York City. They moved to Medford with the immigrant urgency and competitiveness to make a life at any cost. They succeeded, becoming prosperous, and piety mingled with smugness made the whole family insufferably sententious.