Is it possible to make it that group members can invite their friends (who aren't in a group) to a group event, and the friends can attend without having to join the group?

At the moment the group admin can allow members to 'share' the event, but the non-member has to join the group to join the event. But they may not want or need to join the group.

The group admin can control who joins the group, so they can control who joins the event.

However, if group members can 'share' the event, why not allow them to 'invite' their friends with a proper invitation, and then their friends can join the event without joining the group.

Is there a way to make this possible?

Hi, Susan.

This can't be done with a simple hack, I'm sorry... this require changes in core files.
The only thing I can recommend here is to post a request here:

uservoice.jomsocial.com/forums/101561-feature-request