I'd actually have Theis and Tatum both lower and Smart/Jaylen higher.
Take Tatum for example, he just had a great defensive series against Durant but Durant and Giannis are VERY different players. Tatum has a somewhat high center of gravity and has never done great against straight power players. Giannis will go through him, and in the process will put fouls on him that the c's cannot afford. Theis meanwhile will just foul out of the game in about 3 minutes of guarding Giannis.
I think the best approach is put Al, Grant, Jaylen and even Smart on him. Get low, drive him towards the help defense whether that's Rob, Theis, Tatum. Throw some doubles to dig at his dribble on the drive.
If Giannis decides to pull up and shoot against smaller defenders well then you've already won.