Has the invited member access to my Google Drive or his Google Drive or both?
By inviting a member to a team, I believe he/she only has access to the apps in that team. They can still add/edit the info of each sheet connected to those apps, but not direct access to Sheet until you allow it.
Can they create a new app?
Yes, they can
Crystal clear! Understand now that they only have access to their own Google Drive.