Neither is very common, except in speeches given by people learning English.
"There are four people in my family." is a simple and correct expression.
It is probably more common, if you are asked to talk about your family, to describe them:
Some families are simple
Tell me about your family
There's my wife and we have three children
You don't need to say "five people" because we can count.
On the other hand, some are more complex
Tell me about your family.
Well I live with my girlfriend and we have three kids, but the eldest is at university, Katy, my stepdaughter is at high school and the youngest, Jake, is still a baby. Also my girlfriend's mother lives in the annexe.
Families are complex: consider the example. How many people are in that family?
It would normally be "me" because that word is not the subject of a clause. In this respect, English is different from some other languages (in particular Latin and some Latin derived languages). There is some flexibility on this. "It is me." is normal and correct. "It is I" is also correct, but less used. In a long phrase "My mother, my father, my sister and I" could also be correct, but unnusual. English tends to reserve "I" for first-person singular subjects.