Question

why number of family members increase​

Answer 1

that is not true because sometimes it will decrease

Answer 2

Hmm... if it’s a joint family with your grandparents , parents , cousins , sisters , brothers , uncles and aunts , then definitely it will increase , because if your uncles daughter/son is married to a male/ female , then they reproduce a baby , so if everyone in the family marry , they get children and a new family member is welcomed ...