I was looking through your imgur and wow. I really like the Youmu one but, Yuyuko's is just beautiful.
Thank you~! My studio has often been told that the Yuyuko picture is fairly "relaxing," too; one customer actually bought it for his mother solely for that reason~ :3
You're hair and clothes are awesome but sometimes I can't help but feel that it doesn't match other parts of the picture like the skin and background. One example is Yukari's dress vs. the gap she's sitting on.
Funny you should mention problems with Yukari. She actually happens to be an older picture--one of the oldest in the group on our imgur, in fact, next to the Cirno one. I have thought about replacing her with a new Yukari picture for some time now, updating her overall look and making her more consistent with our newer pieces~
The only picture that really stood out as strange to me was the Youmu. First of all I feel like the legs look big compared to the arm and torso. The other thing is that I'm not sure that her stance makes sense. Her right leg looks fully extended and she's really low to the ground, so it looks like she just finished a big strike that she put all her weight behind; however, she's only half way through her strike meaning that the rest of her strike is only powered by her ankle, forward momentum, and arms. My experience tells me that's bad form. Also, her right leg is out at an angle, meaning that after she started her strike she shifted her center of mass to the left, probably to correct and land her strike where she wanted it; however, you wouldn't want to do this because you put the most weight behind your strike by moving straight ahead.
Wow, you certainly got into ripping apart that form, didn't you? Well, I can't say I blame you, since I figured from the beginning that anyone who would know better might find something wrong with it, and that's okay; I still like the picture, though, and she sells pretty well~

Also, Cirno's legs also look too big.
She's definitely the oldest of the bunch by far, and I've thought about updating her as well for some time now, especially considering how much smaller in scale I made her in our latest picture. Not to mention, if I may rip into the same piece for a bit, I'm not a particularly big fan of Cirno's face in that picture, either, but that probably comes from the fact that my studio has gotten a lot better with making more diverse faces and facial expressions since then~
Thank you very much for the critique~!