It is frequent that excess of weight affects to several members of a family, but sometimes, only one child is overweight/obese, while parents and siblings are normal weight.
Parents could be concerned about the effect of dietary changes, particularly on siblings. However, a healthy diet is the same for all children and adults, regardless of their weight. Furthermore, improvement in obesogenic home environment suggests potential benefits to the entire family.
The key is to improve family diet and lifestyles vs dieting, as explained before: selecting high nutritional dense foods while cutting down calories and free sugars, managing portion sizes, avoiding emotional eating and engaging children in more active free-time activities, menu planning and cooking.