Wow I have never seen this topic!
Baldur's Gate actually use second edition D&D rules,so you are right there Malte.
I would say that the whole gang would be either chaotic or neutral good.I think Littlefoot and Cera would fall in the chaotic good,Ducky,Spike and Petire to the neutral good.(Sorry,I started writing this before your post rhombus,but it seems that I agree with you anyway)
For Hyp,Mutt and Nod I would put chaotic neutral,since they just do what they would like to at the given second,bullying in the start,but helping the gang when they feel they should.
For the Sharptooth I would give two algment.If one think that he was after the gang just for revenge for an eye,than I would say chaotic evil.Or,If his motivation was starvation,then true neutral(we never saw him interact with anyone he wouldn't consider snack,so it's hard to tell)
Some more characters I can think of right now:
Grandpa and Grandma longneck:neutral good.They approve laws,and never eager to break them,but in movie 3 they do bend them.
yelowbelly:chaotic neutral no explanation needed.
Chomper's parents:neutral good.They may eat herbivores,but they have to,and they do what is right to do with the gang in the movies.
Mr Thereehorn:lawful neutral,becose he takes tradition above acting good or evil.
Mo:chaotic good,he is helpfull and care about others,and he likes to do what he wants.not what others expect him to do.
By the way here are the alignments if others want to post too
chaotic good:
neutral good
lawfull good
chaotic neutral
true neutral
lawful neutral
chaotic evil
lawful evil
neutral evil