Do I need to resit all of my a levels?

you won't have to resit three because if you get the grades to get onto your course with your two resits it still counts. my brother retook his chemistry alevel and he got accepted with his new grade and the grades he got for maths and physics the year before. also, resitting two alevels is less work than resitting three, so it'll be likely that you'll get a better grade retaking two rather than three.

No, you can retake however many you want.
Some unis do have policies regarding retakes, but none force you to retake all your AL's. Your friend is getting muddled about people taking early exams.

I'm currently resitting two of them but I've just talked to another student resitting and they said that some unis expect you to resit all three ie you can't get 1 grade from one summer and 2 others from the next. I got BCD and am resitting my C and D grades because they're relevant to the course I'm applying for at Uni and I thought B was a good enough grade according to my Uni's entry standards...
Help D: