If I have Skype premium, do the other people have to purchase it to group video call?
Or does one person just have to?
The other people have to purchase Skype premium in order for you to have a group video call. Group video calls are only applicable to premium account and not the free account. Go to http://www.skype.com/en/premium/ for more details.
skype is free on videos call, phone call you have to pay for it.