No! Anyone with the "guest-invite" link to your studio can join your stream without needing to log into a StreamYard account, or download any software.
If you want to require guests to log in, you can turn on the guest authentication in your studio Settings by going to Guests and checking the box next to Guests Must Authenticate. This will require your guests to sign into a Google or FaceBook account in order to enter your studio, and allows you to ban them if needed.
This is what your guests will see before entering your broadcast studio.
If you want your guest to be able to add their own channels/pages as destinations for the stream however, they will need to have a StreamYard account with us and log into it. More info on our Guest Destinations feature here.