Now that Jet blue flies to O' Hare you can geta cheap flight out of Chicago. Get this, you get comfortable seating and free private TV. The inlaws will be impressed without you having to break your budget.
US domestic airlines are all the same. You need to get your inlaws into first class if possible. In coach, the best you can do is get them in Premium economy on United. United has good routes from Chicago to California. Look into buying into first class upgrade or premium economy.