The artwork is really great. My only nitpick is a lack of consistency between panels. Breasts, waists and butts change size and shape without any transformation having taken place, especially for Nicole.
I think it's about time the mom reacts to her face obviously looking 20 years younger and like a supermodel. I mean, really react to it. "Why don't I have any wrinkles anymore? Why do I suddenly have an angular face?" That's not the kind of thing you merely smile about and then shrug off. Also, what would happen if she got doused with the Super Gro formula a second time? Can she become even more youthful and pretty?
It's about time someone figures out what is causing the changes, regardless of whether they decide to tell the others or use it for scheming. It would be a nice change if Luke went all-out on a male power fantasy and sprayed himself with Super Gro, growing bigger and more muscular than ever. Then he could plot to expose his sister to the weed shrinker.