Although you’ve certainly caught something of their expressions the faces have quite a flat look to them. Not a fault in itself as you will see that in many stylised portraits. If you are going for the more ‘classical’ look though, you will have to look very carefully at the subtle variations in tone across the faces and hair to model the three dimensional objects which they are.
The reference is not an easy one to work from. It’s a decent snapshot but doesn’t provide a lot of clues about the actual shapes of the heads.
I’ve stripped some of the paint from this painting and will do more as it was building up to much and will take a new beginning on this portrait.
If you have any observations or suggestions I’d like to hear them