The direct answer to your question is there is an option to RSVP for additional Adults and Youth, however they are not specifically named. While this does give you an accurate head count it does not give you the names of the extra individuals from within TroopTrack for say a Roster. The idea of siblings has been suggested in another thread. Check it out, like and add comment to that one to help push it up as a feature for the developers to consider. Differentiating Scouts and Siblings