Drow abilities

[Myrdin Potter]

Drows have these traits:

Fey Ancestry; ADVSAV:charmed;IMMUNE:sleep

Sunlight Sensitivity; DISATK; DISCHK:wisdom, perception

I am not sure if the save advantage and immune actually does anything or just results in a note. Charmed is an effect but sleep is not.

I am curious about the spells that they get for free. I am not sure how to set the use for the cantrip Dancing Lights. It does not really matter because it is not a powerful spell, but prepared does nothing for cantrips.

[Zacchaeus]

You are correct in that you can't automate advantage on a save vs sleep or charmed. The immunity to charm does work however if you try to place a charm effect on the character.

You don't need to do anything special for cantrips. As you say there's no slots and they can be used at will.