First off, what do you and the rest of your family want to do in Italy? Obviously, visit your husband's family in Pescara, but what else? What do you want to do with your five days on the Amalfi Coast other than Sorrento? Do you want to visit Pompeii?
Plan your trip thinking in terms of nights. For example, two days in Venice could mean one, two or three nights.
If you like ancient (Roman) history, then I would suggest more nights and days in Rome. If you like Renaissance art, then more days / nights in Florence. If you and your family prefer the countryside, then I would suggest that you drop one of the cities (probably Florence) and add some time (with a rental car because it's easier) in the countryside, for example, around Pescara.
To help you decide what to do and where to go, in addition to Rick Steve's Italy, also watch his travel videos. Note which things look the most appealing to you. If you haven't been to Italy before, reading his book will help you with all sorts of travel details.
I would suggest that you put all of your time in Rome at the end, so you don't have to pack and move as many times.
In terms of hotels, what price range are you looking for? You are planning to visit some very popular destinations, and availability over the weekends, in particular, will be low, especially if you want a family room (room for 4 people). Rooms for 2 people are more common in Italy.