] Well, one could also interpret the "and" as a conjunction of two separate things ie the two sisters each representing one or the other vs the combination or blending as you did.

Except that Jane Austen clearly tells us in the first chapter that they both have both qualities:

"(Elinor) had an excellent heart; her disposition was affectionate, and her feelings were strong: but she knew how to govern them"

" Marianne's abilities were, in many respects, quite equal to Elinor's. She was sensible and clever; but eager in everything;"

Neither sister is devoid of either one of the qualities--it is only in the expression and governance of them that they differ.

] While Elinor did keep her feelings in good regulation, do you think she truly learned, by the end of the novel, to express her feelings more?

More than what? She has strong feelings and she expresses them when she needs to express them and in a way that is appropriate. What purpose would it have served her to have put her feelings more on public display? Elinor knew what her feelings towards Edward were, even if she did not demonstrate them as much as Marianne did about Willoughby. Edward would not have been more in love with her than he was. About all Elinor would have gained by making her feelings for Edward more obvious is to have become an object of ridicule when his engagement became known, and an object of even greater contempt to John, Fanny, Mrs. Ferrars, etc.

And, considering the way Mrs. Dashwood has reacted to emotional subjects, it would not have been a good thing to have her mother aware of how upset she was about Edward and Lucy, not to mention that Elinor would have compromised her own integrity by revealing the secret she had promised to keep.

] she didn't get the comfort and advice she needed. She was just left to flounder about on her own.

Advice from whom? What could anyone have possibly advised her to do that would have resulted in a different or better outcome of the situation? Elinor seemed very far from floundering to me.

]it wasn't anything of her doing that assisted her eventual success.

Nor was any of her unhappiness her doing, either. In fact, I have to disagree on the statement. She did contribute to her own ultimate happiness because she had no cause for self-reproach, and self-reproach was something Marianne did have to face with great pain. Elinor also had the comfort of knowing that she had not, in addition to her own pain, made everyone else around her miserable when there was absolutely nothing her mother or Marianen could do to alter the outcome of the situation, and in fact would have probably prolonged her misery the same way they prolonged their own grief and suffering.

] Well, do you think John and Fanny were "happy"? What about Lucy? Or Charlotte? None of these people were particularly balanced personalities but I don't think they suffered too much from it.

This also raises the question of whether what they feel can truly be called 'happiness'. Will John and Fanny ever feel like they have enough money? Will they ever feel they have put his sisters and her brother far enough down to make themselves feel truly superior? Will Fanny ever feel satisfied that neither of her brothers married the Honourable Miss Morton, and one of them married a woman towards whom Fanny feels 'continual ill-will'? Will Lucy and Robert and their 'frequent domestic disagreements' feel like they had found true happiness? Does the fact that Charlotte laughs at her husband's continual insults and the dead plants in her green house make her happy or just an airhead?