Alright lets see, all the renders do not fit. What I mean by that is that they do not go well with the sand background u have going on, you can clearly see that they are just renders instead of one whole image, which is never good. The characters on the right look like they are floating there. I think that the biggest problem is that the contrast between the sand and the renders is too great and the renders will always stick out too much. What needs to be done here is the contrast needs to match and then maybe add like a sand storm effect over everything to blend it in to one image. But that will be tough, and prob can't be done unless you have had a lot of practice with image editing. So there is still a lot more needed to be done here :/
I had a hard time with finding a desert background that matched Red Steel 2's art style, and the closest thing I found was a background from Journey. On a side note if anyone can find a desert background that matched RS2's art style, that'd be awesome.