Hi Sue,
What a neat project!
Unfortunately, the resin is not going to preserve them. The bats need to be preserved before entering the resin. If they are not, they will rot in the resin. You won’t see anything different right away, but over months you will see them decay. Unfortunately, I don’t know how to preserve a bat for a situation like this.
As for the fur, the resin will wet it down like when you get your own hair wet. If you want the hair to stay standing, you will need to rough it up and secure it with adhesive. The gloss sealer spray in our store would work well for this: https://shop.resinobsession.com/collections/tools-and-supplies/products/castin-craft-gloss-resin-sealer-spray
If you try this, would you mind letting us know how it goes?