Design a restaurent reservation programme

Hello, We are wanting to design a simple restaurant reservation programme so our staff can take bookings, which the reservation programme automatically accounts for the number of people already seated: The main purpose of why we need this is to make it easy when taking a reservation and not double booking a table. The design also has to be in a format where things can't be move around by accident by the staff in excel i.e formula's. I have attached a detailed excel programme to show you what we need.