Pisa or Genoa Airport? Which is easier to navigate.? We're seniors.

Pisa is a relatively small airport. As you take your luggage from the pick-up belt you just have a very short and flat walk to the arrival area. As far as I remember, car rentals are near the arrival area.
Departure area is on the same level on the opposite side of the airport.

At present there is a shuttle bus to the railway station as the airport railway stop has been dismantled to build a new people mover, still not ready.

The airport is right by a motorway so it is very easy to drive out of it.

Both are very easy to navigate. They are both small airports. Both have a bus shuttle service to the main station of their respective cities (Genova Piazza Príncipe or Pisa Centrale).
I don't recommend you hire a car while in Santa Margherita. Use the train. You won't need a car while in Liguria. The coast is well served by rail.
.If you go to SML, GOA airport is much closer and you won't need to change trains at La Spezia or elsewhere.

To rent a car for Tuscany, you could rent it also in the city of La Spezia, which is closer than Pisa.

For rental cars use a consolidator. I recommend www.autoeurope.com or www.kemwel.com, two sister companies part of the same corporation.
In Italy they work primarily with Avis-Budget, Europcar, Hertz, Maggiore, which are the largest franchises operating in Italy.
Compare prices with both websites, as they vary.
Remember that rental car companies are franchises. So although they have familiar names, they are not American run companies.

I went through the Pisa airport to CT in October. The airport is small, crowded but easy to navigate. The shuttle to the train station is kind of a pain, but is directly outside the airport, easily found, short walk. You have to do a bit of walking at the Pisa trainstation from the shuttle drop to the station. The Pisa and La Spezia stations both have several platforms (bins) so that will stress you a bit but you will quickly figure out the system. Both have elevators that take you down to go under the tracks and then up when you locate the proper platform for your trip, be sure to note what platform your train departs. Also you can purchase your ticket for the Pisa shuttle from the driver, no need to stand in the long line in the airport for the window that sells train and shuttle tix. view this website for guidance on using the trains and the ticket machines, it was a breeze. www.seat61.com/italy-trains With a bit of study you will pick it up easily. Credit cards can be used in the ticket kiosks and they are English friendly and pretty simple to use. There is also an ATM machine at the Pisa airport on the second floor and a bank window next to it if you have ATM issue, I assume they are the same bank...I used the ATM not the window.

Marie, I'll just touch on a couple points, and leave others who are more knowledgeable to advise about airports etc. You mention navigating with baggage. I hope you have internalized the guidance to "travel light'," as that's very important in most of Italy. You will need to handle your own bags at most points -- in and out of trains and train stations, from stations to hotels, sometimes up stairs, etc. In most cases, reliable assistance is not available. Try to limit yourselves to a rolling carry-on plus maybe a tote bag, for each of you. Also, when you rent a car, there are a number of things to keep in mind. Each driver will need an Intl Drivers Permit (IDP) easily acquired from AAA in the US, to accompany your regular driver's license. Insurance is important. Many of us recommend adding "zero-deductible" insurance to cover you for any damage to the car. Do not count on using your credit card auto insurance coverage in Italy, without conferring closely with the insurance people of your credit card issuer. And, study up a little about no-traffic zones (ZTLs), speed cameras, etc. Have a wonderful visit to these beautiful areas, I hope the weather treats you well!

WE don't speak the language

Don't worry about this. Get a copy of RS Italian Phrase Book and Dictionary. It has all the basics, and then some, to help translate all the basics, along with teaching you "please" "thank you" "train" "bathroom", etc. If you know at least a couple of polite words, Italians are very willing to help you! Most speak some, if not fluent, English.