John Givings seemed more like an Unhealthy INTJ (Type 5), at least to me.
He shows up half way through, see everyone for what they are and proceeds to abrasively pull their heads out of their asses. He had some sort of impairment, however, possibly Schizophrenia or Manic depression.
I don't even care about the others, since he was the best character in the movie.
I think he received an award from at least one major movie critic group for that performance.
I find it hard to type people with personality disorders. In this case, all we know is that John was a mathematician who had lost the ability to think well due to extensive electroshock therapy. It was difficult to determine if his personality was so abrasive and direct because he was J or because of his experiences with his illness and frustration over his losses. It's still not a far cry to think him a more antisocial INTP driven by bitterness and lack of social grace; I've seen it on other forums, even.
In any case, there was even a throwaway joke about the "crazy guy" .... people who are "mad" have often acted as the writer's mouthpiece in cinema and theater.
Helen = ESFJ, I agree with that one. it was ironic to watch her dissociate from her earlier opinions of the Wheelers and turn on them, and watch her husband shut her out because he just tired of listening to her.
not really sure on types for the two protagonists. I see why people have said ENTP, and Frank has some external trappings of that type in how he engages people... but my issue with Frank is that he's played by DiCapprio, who comes across as an F to me and I don't particularly think he's a good actor at times. I feel like his actual personality filters into his character portrayals, muddying type reads. I think with the same script Frank might have come across much differently if played by a more coherent and consistent actor.
There is definitely an E vs I thing here, however. April's definitely an I. Frank behaved a lot more like an EFP type in terms of their arguments, where April was very I. From the start, he could not handle a disagreement in their relationship and would at first try to be nice and over-accommodating, then get frustrated when she did not play along and stroke him, and come after her demanding resolution; she meanwhile needed space to think clearly and felt disrespected and overwhelmed by him and would try to withdraw. The fight at the end was actually remarkable, where he pursues her and then for the first time in his life actually listens to her and gives her space; it's unfortunate that his choice to respect her in this situation, finally, was punished so severely by the choices she used her space to decide upon.
ENTP can sometimes also come across as F, due to extensive use of the Fe function, which they use to engage people and win them over. it's a grounding function for them.
And Frank... You make good points. 
