I can’t say enough about photographic reference. I know you will think this is strange but an artist can make a sculpture look exactly like your loved one from one angle, say the front, but when you look at the sculpture from the side it could appear to be someone totally different. That is because the sculptor works in three dimensions. It is imperative that good photographs are provided to the sculptor from both side and front, in fact as many angles as possible, at the photographs should be at the age that you want the subject captured. If it is not possible to provide this then you must understand the limitations that are set upon the sculpture. You might be able to work with the artist one on one to fix any discrepancies in one view or another but this could take an enormous amount of time and patience and should be clarified before the artist give a price.
I believe it was Rodin that talked about how a person cannot look at a true portrait of himself or herself, because often the sculptor captures so much more than the image. It is true that this may play a part in the approval of some sculpture commissions. But more times than not it is something different entirely.