Ok, obviously it would be best to delve deeply into both Italy and Croatia on separate trips. However, being teachers, we have the luxury of time (to go along with the curse of hot high season travel) so we could spend up to 5 weeks on the trip. So given that time frame, would you consider it reasonably ideal to combine the two (passing through Slovenia, too) and experience some of the commonalities between them? If yes, how best to do it, logistically? What route do you think would be most convenient & practical? PS; we would have our own three children in tow...
You have plenty of time, so yes, it can be done, I have probably done more in less time. As for route, It depends how much time you want in Italy. A basic route might be Rome, Florence, Venice, into Slovenia (maybe more the coastal/western portion) then into Croatia which may include someplace in Istria, Split, Hvar, Maybe Korcula, then Dubrovnik, maybe taking the ferry back to Italy for a flight home. All that is basically a direct circular route; if you figure out the minimum time it would take you for that (by my calculation, at least 3-4 weeks) then you can add days at a location or add a destination to fill in time.