Florence hotel - twin beds!

I assume you're saying you want one room that will sleep 4 people, 2 in twin beds, 2 in a double/queen. You might be better off looking for an apartment. I'm not sure how critical 4-5 star hotels are to you, but if you definitely want a hotel, rather than apartment consider looking at 2-3 star hotels and booking 2 rooms. You probably won't be spending much time in your hotel room, so I'm not sure the upgraded amenities of the higher starred places will matter.
Are you arriving by flight or by train? From the train station you can look at a walk of up to 25 minutes, which could put you on the other side of the river, and have lots of options. You could always splurge on a taxi upon arrival rather than walk with luggage, but once settled in, you'll find you can walk just about anywhere. I find booking.com to be really useful, always select refundable/cancellable (always confirm cancellation dates before booking) and use the filter for beds/bedrooms/bathrooms. The filter isn't perfect but it's a good start.

What time of year are you planning to travel?

Thanks! Yea, sorry my post wasn't super clear! Definitely a hotel with two rooms. We don't really want an apartment. Appreciate the advice!

Here are a few I found when looking for accommodations for four people. I'm not sure how many stars they have in the Italian rating system, but they all get very good reviews. I booked at the first one on the list.

https://www.palazzogambaflorence.com/?act=home
https://florencegrandtour.com/rooms/
https://www.hotelpendini.it/en/index
https://www.relaispiazzasignoria.com/en/appartamenti.php

Hotel Torre Guelfa may fit your needs.

https://www.hoteltorreguelfa.com/en/index.php

Use booking.com to search
Filter by location, budget, #beds, AC, amenities etc

Star ratings in Italy are different than what you are used to for US hotels