It would be more natural to say "I have a four-person family" but what you said isn't wrong either. "I am the eldest brother" is also a more natural way to say "I am the elder brother". Which out of a car, family, and friends do you like most? That's unclear. "In my family there are four members/I have a four-person family. I am the eldest brother. We live in a large house. I have a car, family and friends. I like [the thing you like] the most."