What in your opinion is the estimated height of the (main) 6teen characters?

Yours are almost the same as mine!
Jonesy - 6'3''
Whyatt - 5'11''
Jude - 5'9'' (Not hunched)
Jen - 5'8''
Caitlin -5'5''
Nikki -5'2''

nah i think your estimates seem a bit tall for most of them. I say:
Jonesy 6'1
Wyatt 5'9
Jude 5'8
Jen 5'6
Caitlin 5'4
Nikki 5'1