Running from...

First off, the tiger in the front seem to have more a cat head than a tiger head. The top jaw/muzzle is very thin for a sumatran tiger, so try to make that look heavier. Also, for the line and bump down from the muzzle to forehead, I think you've confused anatomy with style. The line isn't need, as it makes it look rather dog like, and in reality, the forehead slopes down. For the fur on the sides, they look almost, well. . again, house cat like. It is usualy fluffy and doesn't stop at a certain point. [link] [link]

Now, the body. It seems. . . well. . . rather stiff. It has quite literally no neck, which they should have if they are running. [link] [link] It needs to be elongated. And now onto those front legs. They look more like a wolf/cat hybrid's legs than a tiger. Their "elbows" seems very high, but not tucked in. When landing, this is something you would expect. for them to be more tucked into the body. Also, the legs seem very, very thin. Tigers are strong animals with large, thick legs. And also, don't keep them exactly in the same place. It looks more like they are hopping then [link]
[link] [link]
And now the literal body. It looks bloated for a tiger, and I don't know if you used a reference for one or not. I get that they are running, and that they may be heavy, but this is more like it ate more than it should have. The torso is actually pretty thin while running for a tiger. [link] [link]
And the back legs. I really don't know what happened there. The upper part of the leg doesn't really look like a circle. Trust me. Yes, the muscles will "bunch up", but not like that. Look at the references above for the back legs. And again, don't keep them in the same place. It might look better more stretched out?

And for the one in the back. The head looks pretty good, although, don't be afraid to add some lip and teeth to that face. [link] [link] And the body may bunch up, but not that tightly. Remember to add "ripples" or skin layers where the body is getting tighter together.