I have no interest in piling on so I won't - but I visit Italy just about every year. Most years I drive my own car from England, a fair number of the trips have been by train, and I have flown twice.
I usually park the car and take the train once I get to Italy. Can I just give a few pointers if your husband continues to insist on his plan of a "road trip"?
First - you have already alluded to traffic cameras. In the UK they are marked and you are warned. Not in Italy, and not all cameras are fixed locations either. They have a cunning plan called TUTOR where the cameras along a route talk to each other and take your average speed along a stretch. If any individual cameras are offended you get a ticket. If the computer decided you have offended the limit in any averaging area you will get a ticket. Does your husband have a lead foot, or does he just sip at the gas?
Second - I hate paying the high price for fuel here in the UK but at least most distances are really short. Italy traditionally has the highest prices in Europe for fuel, and the distances and speeds (therefore the consumption) are significantly higher in Italy. And many of the smaller filling stations close for the afternoon and in the evening, so plan ahead.
Third - all US or Canadian drivers are required to have mandatory IDPs - International Driver Permits - as well as their home licence. True in Italy, Austria and France; not needed in UK and Germany.
Fourth - (part of first, really) If you rent in Venice, do NOT exceed 40 kph on the causeway. Not even by one kph.
Fifth - unless your children are exceptionally tall for their age they require booster seats in the car, and there are checks. Not needed on the train or in a taxi.
Sixth - don't underestimate the dreaded ZTLs.
Seventh - Are you aware of the myth that Italians drive in the trunk of the car ahead? It is no myth.
Eighth - as you head south you will observe that many Italian drivers treat line markers as non-existent and will go wherever the car and especially motorino fits - or nearly fits.
Ninth - and I know that you have acknowledged this - don't leave anything in the car. And don't open the tail gate after you park.