Invite Question...

Do I need to send a separate invite to someone in the same family (my cousin), if I am not inviting them with a guest or can I just send 1 invite? And is there an age cut off for sending 1 invite instead of 2.

For example:

1 Invite to
The Smith Family

Or 2 invites

1 to
Mr. and Mrs. Robert Smith

and 1 to
Mr. Thomas Smith

Does this make sense?????