That's a bit more difficult!
We don't really "do" valuations here, they're very subjective.
How much you can raise in your shop depends very much on the area you're in and the sorts of customer you have.
If you have rich and generous customers, you might be able to put a good price on and get it, particularly if you can provide this information about them. I'm really not too sure how they would do on ebay, but if you take that route, be sure to include the American market - Caithness is very popular there. However, the worry of ebay is that they may crash.
Perhaps try the shop first?
Putting on my own "bric-a-brac-person" hat, I might try Â£25-30 for each of the leafy ones.
I've honestly not a clue about the Denis Mann ones. You've got good information about them, they're engraved by one of the very top engravers, they're signed and you have a pair. Think of a nice number and try it out on your customers, maybe Â£200 - 250 for the pair?
Display them nicely!
If that doesn't work, you could try ebay - but be sure to have GOOD close-up images of the engraving and the signature marks.
Rubbing a tiny amount of talcum powder over them helps, and take pictures against a black background. Somebody here recently said that using auctivia means you can put in lots of images without incurring loads of charges - sorry, I can't remember who said it, and I don't sell things myself.