Along with this news post, you should state the references to your art up front in some manner. Personal art is understandably left 'uncredited' because hey, it's yours and you're using it yourself. The stock images you purchased and any works bought/commissioned from others needs to be clearly identified as such. Perhaps link these and provide the details under the 'Staff' or FAQ areas. Obviously, stock photos won't have a specific artist, but you can still link the sources and link to the hired artists as well. This can help clear up a ton of confusion about the art.
As far as the dragon is concerned, I agree that a double-check with the original artist is in order. Once you begin collecting money by offering the ability to purchase gold coins, non-commercial use flies out the window. Regardless of the 'free-to-play' aspect, once you begin earning a profit, the entire site becomes a business and therefore, the art becomes used for commercial purposes.
The Griffin I'm a bit sketchy on. Yes, it's clearly referenced from Aywas' Griffin pet. However, the fact that there are so few readily available references of that pose, it's almost hard not to reference it. On the other hand, you did state this; "the only references which were used are photos". It leaves many asking where else you could've referenced the Griffin in this case, as it's a fantasy creature and cannot be photographed.
I'm grateful that you did come and make an attempt to clarify your work. We're not trying to berate or destroy you and your website. Most of the user-base simply wants to make sure that all nooks and crannies are accounted for. The majority here really do enjoy this site and really do want to see it succeed. Do not be offended by our judgements, but ease our minds by continuing to clarify and provide necessary proof.
On a more personal note, I would be very interested in seeing a site artist hired to redraw the items, so that the site is more unique. I understand you not wanting to redraw the creatures that you put effort into personally, but being able to move from stock images to artwork that is unique to the site would be more appealing to those coming in.
"You know what the issue is with this world? Everyone wants a magical solution for their problem, and everyone refuses to believe in magic."
- Jefferson/The Mad Hatter, Once Upon a Time