Geronimo
I don't really see how "people" can be the subject of the verb "to be"...
Okay, first of all, lets clarify what the author intends to say. He does not mean that the family was prominent. Instead, he means that the people, how comprised the family, were prominent. A prominent family is one with, say, 15 members, which is not inline with "well-to-do" as such. But prominent people, say, only 2 members but influential are indeed inline with "well-to-do".
Now when we are clear about author's intent, we can rephrase the sentence by placing the nouns at more appropriate positions without changing the actual meaning as follows:
"Prominent, well-to-do people
have been my family in this middle-western city for three generations."
For the information, the sentence has been taken from the novel "The Great Gatsby", probably from page 2
Hi u r making a very fundamental mistake and it would be good if others confirm .