Order As Many Courses as You Want
Bad Advice: It used to be the diners at a table decided how many courses they would collectively have for their dining experience. No need for this. Order as many as you want regardless of the other guests.
Debunked: Is there anything wrong with one guest ordering an appetizer while the other does not? No. With that said, if someone were to order soup, then salad, followed by another appetizer before their main entree, when the other guests only ordered an entrée, this would be rude. Why? The restaurant will not serve the main course until everyone at the table is ready. This means the other guests must wait while one diner gets through three other courses. Although it is not a fixed rule to do what your tablemates are doing, it is polite to ask the group if anyone would like appetizers. If the group says no, maybe this time you also skip this pre-course.