You could provide the two guests with your planned menu in advance. By doing so, they can adjust their other two+ meals for the day accordingly. For example, if you decide to serve a starch, like rice, each of them can limit their intake of starchy foods for that day so that they can eat the rice at your party. Diabetics can dine just as others do if they plan their daily diet in advance. My husband is a diabetic and this works best for him.
