Power Pack are, for the most part, made from Marvel Legends X-23. I had to shorten the base body to different degrees to get the different heights for each of the siblings.
Zero-G: Alex Power (white) is the tallest and uses the black X-23 as a base with sculpted hair, boots and cuffs. Details are painted. He also has the right hand from Hasbro ML Jean Grey. I dremeled down X-23's chest and added some width around the trunk of the body.
Lightspeed: Julie Power (red) is the same basic recipe as Alex. Although you can't really see in the photos, she has a flexible piece of hair at the back so that she can look upwards for those flying poses. I rounded out her face so that she had a more feminine jawline than Alex but kept the facial family resemblance.
Mass Master: Jack Power (blue) is again the same recipe, but shortened to its limit. I used the purple X-23 face for Jack as he is the cheekier kid and I thought the rounder face would suit him.
Energizer: Katie Power (yellow) is a different recipe from her siblings. As the X-23 body had gotten as short as it really could with Jack, I used a LotR Smeagol figure. This again needed a lot of shortening and dremeling to lose the emaciated detailing. Her head is SOTA Street Fighter Sakura, as are her hands. I think her pig tails are Cammy's. Like the rest of her family, she does use X-23's boots.
I've included a picture of her alongside some of my other 6" scale figures so you can see how they fit in with the rest of the Marvel Legends.
On all figures I tried to go against my usual gritty approach and keep them bright and colourful to get that fun, childish vibe.