Good meeting spot we can drive to from airport in Florence

You say the rest of the family you are picking up is arriving to Florence on Sunday at different times.

Are they arriving by train, by plane, by bus, by car, by space ship, by bike, on foot?

If they are flying in, it would make sense to wait for them at the airport, since you are picking the car up there. If that is the case I would also suggest to meet everybody first, AND THEN, take the shuttle to the airport rental center and rent the car. Driving from the airport rental center back to the airport terminal requires skills few Floridians possess.

One more thing. Unless you are flying in just before renting the car, picking up the car at the airport to go to Grassina is not the most sensible pick up point. If you are already in the city the most sensible pick up point for Grassina (assuming you rent from Hertz) is:

Hertz Firenze Sud c/o, Via Ambrosoli 30, 50136 Firenze FI, Italy
+39 055 095 0022
https://goo.gl/maps/2QJhLC843pw

And from Hertz to Grassina....
https://goo.gl/maps/grEPqo6Wms72

Have to agree with Roberto, it's going to be much easier for the 2 of you to get into the city have the rest meet you there and rent at that location. It took us 3 times around the airport to return our car, navigating out is a mess also. I'm used to driving in cities like Chicago, D.C. Phoenix, and LA.

If you've never driven in Italy before
Please read this and download their PDF.

https://www.italybeyondtheobvious.com/dont-mess-with-ztl-zones

If you're planning on going back into Florence, the Europa parking area is closest to your lodging. Enlarge the map provided by Roberto, and it's easily seen. From there take a bus into the city center.

Is there free parking at Resistenza? I was just looking at the tram website and it talks about paying for the tram and the parking in one transaction. That sounds like there is a fee?

Thank you for the responses.
Some are arriving from Rome by train, some by plane into Florence all on Sunday morning. We don't land until 2:30. We are renting from the airport because we were told the Hertz near the train station was closed on Sunday.
We will be dropping the cars in Orvieto on our way to Rome after 1 week.
Perhaps I should just have everyone come back to the airport? Meeting at the Hertz near the train station not a good idea?

Why not everyone go to the lodging on their own and you just meet them there?

If you arrive on Sunday afternoon then pick up at the airport. All other locations are closed.

Since you appear to be the one arriving last (via plane), ask everybody to meet you at the terminal in the arrival hall. Then you all take the shuttle bus to the rental center across the freeway.

Rent the car and head to the freeway toward Firenze Nord (basically toward Prato).
Follow directions to ROMA.0 to get in the A1. Once in the A1 going south toward ROMA exit at the Florence exit called FIRENZE SUD.
Pay toll at FIRENZE SUD and immediately after the toll booth turn right toward SR222 to Siena. Grassina willl ne on the SR222 just a few km later.

Meeting at the airport looks the best option. Basically, in Florence free and easy parking space is almost unheard of. And among all possible meeting places, the train station is likely the worst, as at present construction sites are mostly blocking accesses so you can easily get stuck in traffic getting there, even on a Sunday. Once there, the only available parking, if any, is in the overpriced underground silo.

Thanks for all your help. Yikes Tom a little harsh? My daughter lived in Florence and I am travelling with close family. We all love to travel and eat and cook together. I have reserved a few amazing restaurants, Lamole, for one that we all agree on. We will also cook together and plan to do so at our villa with the view.
We have 4 designated drivers and purchased the full insurance coverage, no deductible or cost if anything happens.
I do a ton of research to plan a trip, but also like to leave lots of free time to relax and take it all in. We have all discussed thoroughly what our interests are and we are pretty much on the same page but if not there is room and time to venture in another direction.
We are all doing light carry on so have decided my daughter will guide everyone leisurely down through Florence to Piazza Michaelangeo taking taxis at some point if needed. We will either pick them up there or they may just taxi to villa.

Why not have everyone take the #23 bus. Short 17 minute ride. I'd not like to take a 40 min walk with luggage.