The characters that are linked need to be within 5 levels of each other to receive bonus xp. So when you use an 80 you wont get it. If you move your 80 booster to account D, your main acct and slaves A,B,C can get RAF bonus because now they are within level range of each other. Basically you screwed it up. You should have left your main unlinked.

edit: not sure if you move 80 to acct D if your main acct will still get RAF bonus. I think it will because it is still linked with A-C.