If you want to see only rares and epics on your master (A) toon, then do the following.

Set Group Loot.
Set "pass on loot: yes" on A C D and E toon.
Set "pass on loot: no" on B toon.
Set Threshold to Rare.

This way your A toon can see sparkles only on corpses which contain blue or epic items, and you can click the corpses on your A toon, but you need to click Need/Greed/De on B toon, since he is only one eligible to roll. However, if you pass on B toon, then all the toons can loot everything,

Note: There is a visual bug with "Pass on loot", but it works, even though it says in the menu that it remains on No.