PRINCESSES:
For the first princess, the horns are so large that I think adding hair might be good to balance it out a bit.
I presume, for the second one, that you'll be doing a bit more work on the underside of the hair? Aside from that, I like it. It definately needs a mouth added back on, so don't neglect that detail!
The third (tentacled) one looks good, although the the combination of the tongue and position of the model makes me think that she is going to (or is) vomit(ting). I mean no disrespect; it's good, but perhaps if you could make the face a bit more snarly it might counteract that impression. Also, there is a blob (for a lack of a better word) on the top left of her head that is either a horn or an incomplete tentacle; the lack of a second horn-like object inclines me to think that it is a short tentacle that needs lengthening, although giving that princess two small swept-back horns might not be too bad a look.
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SOUL GRINDERS:
Regarding the leg, it is a nice organic take on the Defiler legs. It certainly looks like it'll work well for you.
The pregnant 'grinder seems a bit out of place with the rest of your force, I'm afraid. Overall you have a very low-tech (almost no-tech) force, and she's... well, she's all-tech. I'm sure it'll look good in the end, but I'm not convinced that it will fit style-wise with the rest of the army.
And as for the counts-as... it'll be interesting to see how it progresses. Please keep us posted with updates and WIP shots!