You really need to have the steering cylinder on the port engine either plumbed into the hydraulic system or removed from the motor. Allowing it to move around dry is going to cause the steering to start binding soon. They look like different cylinders so you must ensure that the displacement and stroke is the same on both or there would be problems from that as well.
I would check with Dometic/Seastar to see if your single cylinder can handle both engines. If they are not counter-rotating, you are getting close to the horsepower limitation of that single cylinder.
When you decide if you will be using one steering cylinder or two, then we will need to know the cylinder displacement to select a pump for your application. If you do not know the displacement, you can post a picture of the cylinder part number(s).