There are 4 of us and we will have a car. Where would you think we should look for accommodation in Split as I know it is difficult for parking in the city.

Booking shows that there is over 2000 accommodations with parking. Some are free and on site.
Why do you need a car? Are you traveling on to another place afterwards?

Yes, we will be travelling onto Rovinj.
Without knowing Split it is to focus on a recommended area.

We stayed at the ID Regal Residence located in Old Town just outside of Diocletian's Palace. The room rate includes parking at a nearby parking garage. The manager met us at the garage and helped us with our luggage as we walked to our hotel. ID Regal Residence consists of 4 rooms on the 4th floor. There is no elevator so we did have to walk up and down stairs a lot. But the room was lovely, the location is excellent, and the rate included breakfast every day at Bokeria Restaurant , just a one-minute walk away.

We rented a car in September (Montenegro, Croatia and Mostar, Bosnia). We had a tiny apartment for 5 nights in Split (not suitable for four) near the center. It ended up being next to a public pay lot. We were always able to find a spot there, sometimes requiring one or two swings through the lot, since turnover seemed regular.In one of our walks, we noticed quieter areas, still quite walkable from the center, that appeared to have some on-site parking. We normally look for parking availability on listings on either booking.com or airbnb and then ask the landlords. Driving into Split was not a big problem.