I'll be honest, as a native speaker I had to look up the meaning of impecunious. I assume this is a novel or something like that because this isn't a word most people would know even as a native speaker. It means "having little or no money" and so would be a synonym for "poor".
The last sentence then reads: The [poor] young artist has now become the family benefactor [someone who gives money to help other people or a cause] and that too will give you a quiet little triumph. [the phrase quiet little triumph isn't a common saying, but it makes sense. It would be like a "small victory" something that is a success, and that the person being addressed can be proud of, even if it's not a major accomplishment or something that everyone will know about.
At least that's my take on it.