Unfortunately, you can't please everyone, no matter how hard your good intentions. As others have said, it is your restaurant, therefore you get to make the rules.
Anyone who has taken a few minutes to talk with you or just observe how happy your wait staff is or how much you seem to enjoy when your customers are having a great meal will recognize your true intentions. Most people that have either dined there before or see how small your restaurant is despite the great reviews should see that your efforts are about pleasing people and giving as many people the opportunity to enjoy as possible, not to maximize profits.
With that said, you do create a dilemna ... by having so much good food I tend to over eat. Once that takes place and my over stuffed stomach finds a way to still squeeze in that wonderful key lime pie, I then have the difficulty of trying to figure out how to get up so that others in waiting may come in and enjoy themselves.
Seriously though ... your phone message already indicates how small the restaurant is and that you are trying to do the best you can. Your menu has some verbage about the small operation. At this point, just ask people to be patient and polite and if they can't or won't, they may be asked to leave. There really isn't anything else you can do (legally).