How can I shop wisely for foods that are okay for family member with diabetes?

Most important thing. Of all is please try and purchase complex carbs, the darker the better. White starches are a big no no. Of course, protein, good fats and fruit veggies and other high fiber foods are excellent, healthy choices.
Nothing in excess. If someone in your family has diabetes, things have to be altered, but not totally changed. The type of diabetes is also important. Type I is in younger people, and they need Insulin for nutrition, so sugar must be controlled, but they need all foods to grow. Type ii are older, and need drugs to help their Insulin work. They need to cut out sugary foods and extra food to get weight down.