I am assuming they are already skinned and fleshed out.
When I lived in Arizona I preserved a great many rattlesnake skins and usedthem for belt buckles, hat bands, wallets, etc. I brushed on a 1-1-1 mix ofwater, glycerin, and rubbing alcohol using a paint brush. I usually gave them about three coats,letting them dry between applications.
You may have a problem with the scales falling off as time goes by; in factit is better to brush them off before applying the mix.
Tandy leather used to sell NeatLac (sp?) which was a spray on coating thatgive the skins a high gloss and really brings out the color.
I have many items that I have made over the years and they all still lookgreat.
If all you want to do is hang them on a wall you could glue them on a backing, like felt, with contact or leather cement. I used to use contact cement and Leather Weld. If they are still plyable (sp?) you might be able to sew them on with a common sewing machine.