Pat, welcome aboard Cruise-Chat.
I did a crossing from Ft Lauderdale to Lisbon a few years ago and loved it. Mornings were cool but not cold, afternoons warm and sunny. The outdoor pool was closed (this was an older ship) but there were other things to do both outdoors as well as indoors.
As you can see by my ticker, I'm booked to do another crossing this spring. It will be on a smaller (200 pax) ship but I'm really looking forward to it.
If your parents enjoy days at sea, they should have a great time! Why don't you join them???