You MUST add 20% to Google drive times to reflect reality - and I don't care how many drivers you have, trying to go more than 600 miles in one day with NO sightseeing or getting off the beaten path is NOT a wise idea.

Fresno to Columbus via fastest route is 2330 miles and will take you 4.5 days. Fastest route:

CA-99/CA-58/I-40 to Memphis
US-78 (I-22) to Birmingham
I-65 to Montgomery
I-85/AL-186/US-80 to Columbus

The southern route adds 60 miles and 3 hours, bypassing LA:

CA-99/CA-58/US-395/I-15/I-10/I-20 to Meridian
US-80 to Montgomery, then as above.