Two nights at the beginning of your trip means really just one non-jetlagged/sleep-deprived day. There's a limit to how much traveling I'd want to do for just one real day of sightseeing. Much as I think Ravenna is wonderful, I don't believe I'd choose it in this situation. It would be a minimum of 3 hr. 50 min. by train from Malpensa. There would be two or three transfers required, so (jetlagged though you might be) at least one of you would have to remain alert and get everyone off the train on at least three occasions. It wouldn't be prudent to buy the train tickets in advance, so you'd most likely pay at least 60 euros per person from Malpensa to Ravenna. The trip from Ravenna to Florence would be faster (just over two hours, probably) and less expensive; you'd be able to plan ahead and buy those tickets in advance, saving a bit of money on the Frecciarossa leg of the trip.
Bologna has a large historic district that's interesting for wandering around. Basing in Bologna for your first two nights would minimize the time spent on trains since it's on the Freccia line between Milan and Florence. If you happen to be energetic enough on your arrival day to see a good bit of historic Bologna, you'd have the option of taking a day-trip on Day 2 since Bologna is a major transportation hub. There's plenty in Bologna to occupy you for 1-1/2 days if you opt to take it easy and stay in that city until you head to Florence. I enjoyed the walking tour offered by the tourist office, which I took in 2015.
