I don't mind them being a little bigger than typical, esp if they were older and fully grown, but the size of a small truck... eh, no. Maybe keep them at or a few inches below average adult human height
at most. None of this 6' and over business.
Definitely some conflict between the scenes of them as kids -- What were they, around 8? 10 at most? -- and the present day size of them when they're still supposed to be teens; or so they claim. You tellin' me in that short handful of years they grew and changed
that much?

Puberty happens, sure, but god damn, I don't care if your
are mutants, no one looks like a 30-year-old spending too much time at the gym when they're still a teenager; the fully adult body just isn't there yet.

(Which is why they're adults in my head, no matter what those two movies claim.)
I'd say shrink everyone down to about Mikey's height at most. If there's anything he got the best of in these, design-wise, it's that he's the smallest of the bunch and not so overwhelmingly large.