Can my guests add other guests?
Nope. Members own pictures, guests are just that. If they want to invite a "+1" they'll need to ask you, the member 😉.
No. Guests cannot see who other contributors are, nor can they add or delete them. If they're contributing guests, they can add and delete their own comments, but they cannot delete comments the owner or other contributors have made. If they've been invited as a viewer only, well, that's all they can do.
As a member, you're the boss of your own pictures and albums. Learn more about how accounts work.