Hello and welcome to what will be a general archive of who is whom.
I will make a separate one for each Family, and as of right now, each family is assigned one number, and its subsequent family units will add onto that number.
The original Rostand Family's number is 1, and that of the family unit of their firstborn will be 1.1, their second child's will be 1.2, and once 1.1 have a family on their own, they'll be 1.1.1, and so ad infinitum.
Feel free to ask any questions you may have, I understand just how complicated this seems to be.
If the children of 1.1.1 (in example) were to lost the surname Rostand in favour of that of their spouse, their descendency will not be recorded further, unless they have married into an affiliated family or a branch one, which are those of travelers with no other relatives.
A number will be then tackled to the family name; that way the Evans branch of the Rostand Family is assigned the number 2.