I also recommend reminding everyone at the airport. I have had problems with being "forgotten" when getting off a plane, or being given an airline w/c and told that someone will be be along to push it and they never showed up. The last time I flew they tried to convince me on two different flights to just walk off and find a w/c in the terminal because they didn't think anyone was going to come get me. Sorry, not happening! The pilot almost ended up going to try to find a chair to wheel me of!
Tell them when you check in that you have people that need assistance. Tell the gate agent. Remind the Flight Attendant when you get on board. And then remind them again a little before you land-- particularly if it is a long flight. They can call ahead and make sure that things are in place.
I always have it on my reservation, but have still found that I need to remind. I am very polite about it and have never had anyone get annoyed that I reminded them.
Also if they might need assistance getting on to the plane you can request a w/c to take them on the ramp to the door of the plane. The angles of the inclines on some of the jetways can be very difficult if you have balance issues. Also let the gate agent know if you want to preboard so you have a little more time to walk to the plane and get settled.