Assuming you have a handicapped placard, your husband can either get out of your vehicle at the curb when you drop off your luggage or stay in the car and both get out in the parking lot. For me, as the disabled person, I would rather wait and get out in the lot so I can take my time and get situated. That’s less stressful to me.
As for assistance, that will depend on what your husband needs. If he is always in a motorized w/c he can most likely just board whenever your boarding group is called. The only reason you would need anything different is if he needs someone to push him other than you. My sister had to use a wheelchair on one cruise and we just pushed her onto the ship. Another time, I was just using a cane but couldn’t do the incline on the boarding ramp so we did get assistance from port/ship personnel.