In your above scenario, if all thats in the party is A D & E then yes it will work (since the ones linked to A (B & C) are not present). If you were to have all 5 in a party only D & E will get the xp but not A(lvl70), B & C but since you'll just be giving them free levels it will work the way you want.

A boosts D & E, D & E grant levels to C & D, C & D are never boosted by A.