The points that your brother received on his provisional moped licence will be carried onto his car licence. Since he has exactly 6 points on the provisional licence, he can still do his driving test and if he passes, he will get a full UK driving licence. However if he gets any other points, his licence will be revoked and he will have to start the whole process again, that is, apply for a provisional driving licence and redo all the tests once more.
As far as insurance is concerned, he will have to declare the penalty points that he has on his licence as insurance companies want to know this information for the last 5 years. This will mean that his premiums will be much higher than the average.