Until the spell ends, four willing creatures you touch have resistance to psychic damage, immunity to the charmed condition, and any effect that would sense their emotions or read their thoughts automatically fails unless the source of the effect is a spell of 6th level or higher, even if the spell is cast using a higher level spell slot. 

At Higher Levels. When you cast this spell with a spell slot of 6th or higher, you can target one additional creature for each slot above 5th.