The Druchii and the True Kin are only really close in that they are both 'dark elves'. Druchii society is very regimented and orderly, with strict hierarchy and behavioural codes. They also follow a singe ruler, the Witch King. That's a stark contrast to the anarchic lifestyle and fractured allegiances of the True Kin. It's true that both favour underhanded means of advancement, but there are certain rules to it. It's seen as taboo for a Druchii to kill his own family, for example.
Where the True Kin fear Slaanesh, and strive frantically to extend their lifespan to delay falling into the clutches of She Who Thirsts, there are some Druchii who actively worship her. Indeed, the Cult of Slaanesh counts many nobles amongst their fold, including Morathi herself.
They do both love torturing and enslaving folk though.