If I have apple TV on my iPhone, do I have to pay more to watch movies on my MacBook? Is it a different account?

if you mean you have a subscription to Apple TV Plus, you can access this across your devices signed in with the same Apple ID you subscribed with. However, Movies that say rent or buy are from the iTunes Store and not free. (Apple TV + is Apple Original content).

if you purchase, subscribe or rent content via Apple you can view it on other devices signed in with the same Apple ID

If you are signing in with the same Apple ID then they would all be accessing that same account and be able to view the same purchases/subscriptions.