I think Isabella was very insincere and never in love with either James or Capt Tilney. I see Isab as an unsuccesssful Lucy Steele -- I don't believe Lucy was in love with either Edward or Robert but went after the richer brother. I think Isab did not intend to break off her engagement until sure of Capt T, but was forced to do so, becasue James was there, saw her flirtation with Capt T and remonstrated with her (Edward was not present to see Lucy's behaviour with Robert).

I don't think Capt T was a complete villain eitehr, after all, his brother and sister were fond of him, and worried that he might have been ensnared by an unprincipled girl. But Capt T was smarter than the foolish Robert Ferrars. He was "lively, sometimes thoughtless", but with "a stronger head". Capt T would have been a brilliant match for Isab, but even James was a fairly good match for her -- Mrs Allen spoke of Isab's good luck on becoming engaged to James, Isab herself was entirely without fortune.