GroupCast - Is a concept comes from talk in the crowd, when you adress 2 all with "high voice" or even with a cry =).
Other description of GroupCast IS "directed spam".
4 GroupCast request U must DEFINE:
Personal profile of crowd participant, that reply to your question
Croud persons from your contact list.
KW in your question 2 describe NEEDED personal skills of person in Group U will cast