Eight of us are taking a cruise with a stop at Grand Cayman. I would like to go to Seven Mile Beach for the day from our cruise ship. Are there beaches or resorts that allow public access to those not staying at their resort/ hotel. We would really like a chair and umbrella and understand there would be a fee. We are sailing on Feb 8, 2109.

The answer is yes. Royal Palms rents cabanas with 6 chairs and 4 beach loungers for the day for $125, but you have to make a reservation, and you need a credit card: https://royalpalmscayman.com/cruising/

The aforementioned Royals Palms is one place to rent loungers and umbrellas (no reservations needed unless trying to score a cabana) and on the Public Beach section of Seven Mile Beach near Calico Jacks is the other.
Calico Jacks @ Public Beach

I can agree with the other posters, those are the only options I am aware of currently.