I have no idea how erhu bridges are commercially made. I have made quite a few by carving, experimenting with different woods, shapes and sizes. One thing I have noticed is that a hole "opens" out the sound.
At a minimum, you need a drill and a chisel/knife, and small blocks of wood.
Useful tools: saw, for cutting small pieces from a bigger bit of wood gouges, for creating concave surfaces and also the circular base. needle file or sandpaper stuck to sticks, for smoothing off facets, although I prefer the finish left from a sharp blade. bench hook or similar, somewhere where you can put the bridge and push your chisel against.
Also useful is a means of holding the wood for drilling.
Over the last few days I tried a few on the 8 sided erhu as shown in the pics. The maple ones tend to emphasis the treble with a raspy hollow sound. Ash, mahogany and beech are quite trebly but seem a bit more smoother.
I took one of the ebony bridge: the right one of 3 ebony bridges in the first pic, and back row 4th from left in the last pic, in the original post, and made it smaller but still quite tall. On the right in the following pic.
As for sound of the three, the biggest bridge on the left sounds more muted and smoother but seems not clear, and less loud. It does sound like vibration is being absorbed.
The middle one I think I bought but I'm not definite on that and in any case I glued on a bit of ebony on top, the colour is more black with the rest of the bridge being a dark brown. It's the smallest of the 3. Sound is quite raspy and trebly. It's louder and more vibrant but sound "hard".
The right one sounds in between, smoother but still "hard" sounding.
I've gone back to using the bridge I was using before, I think it's rosewood.
I also tried a rosewood bridge in different shape and size (front row left in 3rd and 4th pics in first post) and that sounds thin, raspy and hollow. I think size and amount of wood makes a difference, as well as the type of wood. Eg maple might need to be bigger than ebony to give a fuller more balanced sound.
All this is on one particlur erhu, one bridge could sound very different on different erhus. And of course the damper can change the sound a lot. I think my erhu tends towards a thin and hollow sound.