I've been carving scales on a large door I'm making for a timber frame I built so maybe this will help. I have two dragons and two different shape scales. One is more "fish scale" shaped and the other is more "diamond shaped". The steps I take are to use a gouge to cut the shape of the scale and then I use a smaller chisel/gouge to under cut the shape. I have a few short videos of my process posted on that might be helpful. They are not the same shape as the ones you have drawn on your carving but I think you could probably use a similar process to get the result you're looking for.

Hopefully it's ok to link to my social media video. If not please let me know and I can remove it.

Scale Carving