My only advice is do not be bound by your reference photos for composition. That is not what they are for. You are free to move figures around change the position of hands. You can use a figure in one that is in a better position. Remember you are not a portrait photographer so you are not bound by the image the camera captures. Take your reference and draw some compositions using the photos as reference. Then once you have a nice composition at the sketch stage take it to a more complete sketch. Then do some studies of the heads and maybe the hands if you have to change them for better expression.
Also, you can take other photos under similar lighting of hands as reference. This is a very complex painting, and to pull it off without doing all the necessary preliminary work would be very difficult at best. I feel you have some good reference to get a start with. And you have the drawing and painting skills to make this a very interesting painting, so don't take shortcuts and end up with a painting that is less then you are capable of.
So get drawing. Then once you have the composition you like then do a re-shoot if need be. You will probably find you need reference you don't have so I would plan on it.
I have never done a portrait like this but my illustration background and the planning demanded by art directors in some was helped me develop a system. It always starts with a bunch of sketches way before I ever take a single photo. And usually I then do a few more detailed sketches to submit to the AD. And once a composition is approved I am bound to that. And any changes I must resubmit for approval. Until I know what the composition is going to be, I have no idea what I need for reference. For illustration work, I often had professional photography done and their time is money. So you don't waste a photographer's time taking shots you are not going to use. And you do not want to have to call them back to take shots you need but did not get.
I take most of my reference shots myself now, but I still start planning the composition before the photo session. As a portrait painter, you have much more control. You can change whatever you want at any point. So even if you have finalized a composition, but later see a way it could be better, you don't need an AD to approve the change. These images give you a lot of choices. I can't see from the images posted if they have enough information for likeness on all the figures but I assume that the originals are of a much higher resolution and offer more detail. So do a lot of drawing I am sure you can not only pull this off, but make it a flagship piece in your portfolio that will lead to more multi-figure commissions. What joy - right - just think you can look forward to more headaches like this.
As for what the father said he wants that is his minimum request. You do not strike me as a person that wants to do just enough. Exceed his expectations and make this a painting you can be proud of not just now but years from now. Remember we can recognize a person across the street that we know. Likeness is not all in the details so even in this painting you should strive to capture a likeness. I wish you all the best on this.