There are no restrictions on the number of passengers a provisional licence holder can carry in a car within the normal limits that would be expected for that category of car.
What you do need to ensure as a provisional licence holder is that the car is insured, thus covering the passengers, and that you are being supervised by a full british licence holder. If you do carry passengers make sure there are no conditions on your insurance restricting you carrying passengers, that the car is fully road worthy and has a current MOT certificate.
Any responsible provisional licence holder will always abide by the terms of the licence, not drink and drive, drive without insurance, or drive unsupervised or without displaying 'L' plates. Speeding is also something a provisional licence holder should avoid, as these could cause you to end up with penalty points on your provisional licence.