@cstiehlSolution for Disadvantage + Lucky Feat: PC picks 2 of the 3 d20 results. Lowest of those two is used. That would work. Or roll two, take the lowest, and then roll the third die and pick one.
— Jeremy Crawford (@JeremyECrawford) May 19, 2015
This has been clarified in the Sage Advice document on dndbeyond.
https://www.dndbeyond.com/sources/sac/sage-advice-compendium#Lucky