Looking good! I can already tell that these are going to be great characters and (if you accept the concept of 'Character First!' great characters tend to lead to great storytelling. You are well on your way!
The texturing is really starting to look great as well.
I'm not smart enough to accurately convey what I want to say about proportions here so I will type toward it and hope others can narrow my focus. Ultimately this is your story to tell and I am not trying to sway you from pursuing your vision in any way. I do want to offer feedback for consideration. I hope you will do the same for me someday.
Here's a site I found while trying to find the right words to say:http://www.zebtoonz.com/proportions.htm
There's nothing there you don't already know already right?
The area that comes closest to what I'm rambling on is somewhat hidden in the webpage:
You also need to establish relative sizes between each character, i.e., Adults are one head taller than a ten-year-old, almost two heads taller than a six-year-old, etc. It's helpful to do a character sheet with all your characters on the same page to show comparative sizes.
Obviously this is that artist's attempt to formulate his own understanding on the relative proportion of characters. Your mileage may vary. I've certainly seen adults that towered a lot farther than one head above ten year olds. While much rarer, I've seen shorter ones as well.
What I'm after here is a sense that the characters belong in the same set... in the same universe... in the same story. Can they can safely and effectively interact (this will make them easier to animate!). When they are in a close up shot, establishing shot or looking eye to eye does everything work... in frame? Are their silhouettes immediately recognizable and compatible. If they were seen only in black against white how might their interaction 'read'.
So, this is the underlying area of focus I think... I think... I am narrowing this down to:
Why are the head proportions so dissimilar between the two characters? Should they be more similar? If not, why not? Will it have impact on your storytelling one way or the other? (i.e. There may be very good reason for this or even a greater dissimilarity)
You don't have to answer these questions here. The important thing is just to ask yourself these design and composition related questions. I'm certain you are already. If you are happy with the relative proportions between the characters as they are then that is an answer in and of itself. It's your thing... "Please yourself."
My long winded way of saying... I'm enjoying your updates!
Added: Here is an old classic from Preston Blair: