Composing group portraits is an enjoyable and interesting challenge. It is not easy to create a natural looking group in a painting and an artist who is truly good at it is worth searching for. There are not that many. Most portraits are of single subjects.
There are many ways to arrange a group of people – formally, informally, posed as for a photograph, relaxed as though sharing a moment, perhaps listening to music, playing a game or gathered for a meal. The mood will depend on whether you are creating an informal family portrait or a powerful corporate statement.
For many years, group portraits tended to be lines of people, each person the same size to give equal emphasis, then Rembrandt came along and changes the rules (and it was not universally appreciated). Since then, many artists and photographers have worked hard to expand what a group portrait can be.
When choosing your artist to paint a group, take a good look at the groups they have done before – how confident are they in handling this challenge? Are their group portraits consistently interesting in ways that you like? Group portraits tend to be assembled from many photographs or separate sketches of the individuals in the group so it is important to see a preparatory sketch of how all the elements will be fitted together before the final painting commences.
Experience really helps in solving the problems in group portraiture. You will recognize experience when you see it.