What's the point of having the same site on both wildlife art domains? Need to ditch one of those - the .com is doing better so keep that and 301 redirect the .co.uk to it.
Personally I would scrap them all and work it like this:
1. Use your personal domain to host a personal biography and portfolio examples - use this to detail the work you can do and how people can get in touch, etc.
2. Use either
http://www.wildlifeart-online.com/ or
http://www.onlineartdemos.co.uk/ as your main shop area. Which you use is up to you (I'd personally go with the online art demos one).
3. 301 redirect the remaining domains to the main shop site you choose.
By 301 redirecting the unused "link weight" from them to your main site and it also means Google won't list them in the index (which is a good thing).
You're not in any serious trouble so I wouldn't panic, but it is certainly something you want to sort out.
Scott