Just watched this classic again last night
Maria is definitely an ENFP and I do like ISTJ for Captain... complete oppisites haha XD
Anyway, the Baroness I think is an ESTJ. Uncle Max is almost certainly an ESTP hehe
And the children:
Liesl: IxFJ.... It's hard to say- she's quite openly affectionate and motherly towards her younger siblings (F... well, Fe for that matter), but she's not super talkative or particularly energized by other people (I). She's a hardcore romantic (NF), but she did seem to lack the insight to see that Rolf's radical nazi ideas will eventually cause a major rift in their relationship, and that it wouldn't work out so she probably shouldn't be singing about devoting her dependance on him. However, I'm willing to chalk that up to inexperience (she's only 16 going on 17 and totally unprepared to face a world of men she is!). I think the difference between her N and S comes down to the reason she stayed with her family rather than kicking up a fuss about being with Rolf- because of her own strong-willed conflicting ideas and opinions (Ni), or because of her loyalty and values (Si). It could even be both equally. That's why she's a tricky one
Frederich - ISTJ... One of those ones with a tough exterior and a heart of gold. (while his values are his driving force, they're subconsciously kept in the background so he can get things done more efficently, giving that 'tough exterior/heart of gold' persona) ... He seems to have looked up to his father (also an ISTJ by my book) before his mother died by adopting his values, traits, ways of thinking, etc... but of course, when his mother died and his father completely changed, poor guy was quite lost in his development as a person.
Louisa - ISxP... Remember when Maria went off at the Captain for not knowing his children, and she said 'Louisa notices everything' -- that, coupled with her rebelious, daring nature spells out SP for sure

I'm not really sure whether she's a thinkerer or a feelerer. If I had to go with my gut, I'd say ISFP... because she holds a grudge on all Frualeins in the world, she commits the most violent acts toward them (the frogs and snakes in pokets and the jar of spiders in the bed... like any good ISxP, she has an army of animals at her disposal hahaha

), and it seems to take her the longest to get over it, which is, I must admit, is an Fi-dom weakness. But any type can hold serious grudges, which is why I've refrained from typing her as one or the other
Kurt - ENTP - He's curious and playful, and determined to get the answers to whatever questions he might have, like when he made Maria dance that Austrian dance with him at the ball. I'm actually not sure if he's more Extroverted than Introverted, but he does seem to get more energy from being in the company of people than the others.
Brigitta - INxx... Hard to say, but seeing as how reading is her favoured past time and she enjoys being solitary and smart, I'm leaning more towards INxx than ISxx- but mind you, there are plenty of S' s out there who favoured reading and other intellectual persuits as children, so as you can see, it really is impossible to say. :/
Marta - IxFP... she seems more maternal, kind, and gentle than most of her siblings, and more sensitive than any of them, so I'm leaning towards her being an Fi-dom. However, because of her age (7), it's hard to say. :O
Gretl - ENxP ... an induvidualist for sure - not every kid can completely ignore the feeling to conform to the opinion around you and then boldly state their own in front of everyone (when everyone hated Maria in the beginning, she went up to her in front of them and gave her a hug and told her she liked her). I'm sensing more N than S here, since her actions are almost always based off... well, no visible reason at all, but rather, her gut. She instantly trusted Maria for no reason at all and 'knew' they were going to make great friends.... when she'd only known of her for about 2 minutes. However, I'm hesitant to chalk it up to personality as it could also likely be a 'child's instinct.'