Hi,
What a lovely surprise! You can do this with one 22" and a small daybag both CARRIED ON! Laundry is your friend! :)
Don't worry about standing out as tourists....be comfortable and travel light, take at least one outfit that can be used for a nice dress up dinner..even his hiking pants can be dressed up with a nice shirt...button down shirts are cooler than polo's and t shirts..so pack one for him. I suggest one travel shirt with mesh panel which keeps shirt from sticking...Columbia has some solid colors or plaids that don't look very Amazon Jungle LOL...I also like them for the hidden zipper pocket.
I have been to Italy many times and a few of them in early July... it will be hot, lik Arizona HOT...so a hat yes, a plain no logo baseball cap is fine for either of you, I am very fair and always take a packable bamboo/cloth hat that covers my neck and ears.
Sunscreen start off with at least 2 bottles of 3 ounces as this is the minumum for two people on the first day...then buy some.
As long as your husband will wear pants each day, as this is required for visiting churches and some other sights. Knees and shoulders covered for both genders. He may benefit from zip off just for this reason.
IF your husband will wear sandals or boat shoes ( kinda flat and cobble stones are HARD) bring ONE pair, 2 pair shoes total...sneakers are fine, darker are better for nighttime ...one pair of flip flops will pack flat and work well for beach and slippers for hotel. If he likes sandals, then a pair that is cushioned with one pair of sneakers could work well for him.
For women: I always pack a thin scarf, you will probably buy more there! AND a sarong, very light weight to wear as a long skirt/cover up when visiting churches, can also be used as a ground cloth for beaches,picnics or sitting on steps, or a wrap on the cold air planes, keep it in your daybag.
This has been my companion on many trips for 7 years...Bra stash with two straps..it attaches to the bra strap. The one with a single snap is a horrible design you will lose it...I do not recommend.
.https://www.amazon.com/Nude-Pocket-Travel-Safe-Wallet/dp/B000BQW8AS
I attach it to ONE side only and tuck the pouch into my bra under my arm..you won't feel it as long as you just keep ONE credit card and some day cash, keep the rest of money cards and passport under clothing in larger pouch...this enables me to not worry about pick pockets but be able to reach in and take out what I need right in shops...and it is attached so no one can snatch it and I won't place it on a countertop...where many wallets are stolen...I just make a joke with the shopkeeper about " going to the Banco di Napoli" as I take my credit card out...they love it! :)
Enjoy your trip!