So, I agree with the previous comments about how the colors and overall composition is excellent. However, I feel the need to be that person and critique a few things.
First of all, I own whippets-- Which is the main reason I feel the need to be this picky. In general the ones in the back are a tad bulky. If they are racing whippets then yes they do bulk up, and so do bullies (however you definitely did not draw bullies). For the most part that I have seen, if they do bulk up they do not appear to be quite as ripped, especially in the neck and shoulders region (by ripped I mean the fact that their necks bulge out so far from the shoulders so it looks dislocated). Also their back legs should be about as tall as the front, so there is little to no decline in height from front to back. If they do have a spinal curve bump, it is further down the back just before the under-tuck as the rib cage ends. However, the "bump" is more of a gentle slope, rather than a true "bump". The main issue that I see is also the lack of gentle curves. I recognize that they are stylized to a degree, however to go with the realistic quality of the rest of the piece they need that extra bit of grace that is a characteristic of almost any whippet. For example, the top whippet on the far right side has a severe under bite, and I would go so far as to say it looks as though it is lacking a lower jaw. However, if the line from the tip of the nose had been gradually let down and then brought back to the cheek it would be more anatomically correct, rather than bringing the nose to a point. Pretty much I would suggest taking a look at some more pictures of whippets, and observe the details that give them their true characteristic form. In particular look at the head, neck, and shoulders. You've almost got it, the whippet on the lower right next to the woman is the most correct.
The second thing is foreshortening. The whippet in the far back is the same size as the ones in the front. Likewise the candles remain the same height, except for the correct one past the bridge. The woman's feet are also confusing because they are both the same size. It is hard to tell if the foot in front is attached to the hip closest to the viewer, or farther back. Past the bridge looks fine, it's just the gradual recession that looks a bit off.