I have been commissioned to paint 3 siblings in one portrait and need some pointers, especially with composition. The client has limited wall space so it will not be a full length portrait but probably waist up. Do you put the shortest one in the middle to avoid the triangle effect or will your eye travel easily from one to the other if the tallest is in the middle? Are there definite "don'ts" with this type of portrait?
Would enjoy reading from other artists how they have approached this. This is my first attempt with oils for 3 in 1 painting and I am a little nervous about doing a good job. Any advice is greatly appreciated

Thanks!