See below--do I need to enter all new e-mails, or can other relatives invite relatives in?

I have many first cousins.  I am creating the tree.  I don't know all of their e-mails.  When I invite one to join whom I know from a particular family group, can she invite her sisters in (also my first cousins), or do I need to get their e-mails from her and invite them myself?--Helen (Lyn) Ward Page