At the beginning of nearly every table service meal at WDW, your server will ask you if you are participating in the Disney Dining Plan. At this time, yes, you should tell your server that different members of your group are on different versions of the plan. The server will make note of this and each person will receive his or her allotted dining plan benefits.
You are correct that the basic dining plan does not include appetizers, which the deluxe version does. You can read more about this
HERE. You should know that the members of your party on the basic plan are welcome to order appetizers, but they will need to pay for them out of pocket.
It is perfectly fine for people on different dining plans to eat together. It is also fine for non-dining-plan people to eat with dining-plan people. But please inform your server of the situation AT THE BEGINNING OF THE MEAL.
Enjoy your stay at Walt Disney World.