posted by John .
1. How many are there in your family?
2. How many people are there in your family?
3. How many members are there in your family?
Are they all aceptable?
Which one is the most common?
They are all acceptable. No. 1 is most common.
The word "there" could be omitted in each, but it is probably best to leave it. When responding to the question, "There are.." would be the appropriate beginning.