First of all you will need to cut the scales from the slabs. Once you have done so and start sanding them to size, shape and design, as they seem thick, the scales might warp a bit.

I use a standing steamer myself to straighten them. Or you could just boil some water and use the steam. Depending the direction you hold them they will straighten themselves back. It's really not that hard. I like to nourish them with neatsfoot oil myself.

You should be fine moving forward.

BTW, these are some fine looking horn slabs