folder , subfolders and files permissions

Hi ,

I have a folder named MainFolder withe permissions for 3 users (A , B , C)

In this MainFolder I have around 10 SubFolders and in each subfolder there are Files.

I want these 3 users to have access on all these subfolders and files except 1 folder which I want to put special permissions for 2 of them.

What happened is that I messed up a lot with permissions and it becoming confusing.Is there a simple way to remove all permissions and redo it again in less time?

Note that the MainFolder is in another shared folder which have permissions for others Users including the A, B,C.