I thought I'd look to see what are the first words or conversation given the anti-hero and anti-heroine. Often in Austen the first words given a character are significant. It's as if she's setting a song, and strikes a central note to start with.
The two first conversations are about marriage. In the first it's a case of badinage on the part of the two. Mrs Grant says she would like to have her half-brother and half-sister settle near her, so Henry must marry the youngest Miss Bertram "a nice, good-humoured, accomplished girl, who will make you very happy:"
"Henry bowed and thanked her.
Mary teases that if Mrs Grant can "persuade" Henry she has all the address of a French woman, for she has "three very particular friends who have been all dying for him in their turn; and the pains which they, their mothers, (very clever women,) as well as my dear aunt and myself, have taken to reason, coax, or trick himinto marrying, is inconceivable! He is the most horrible flirt that can be imagined. If your Miss Bertrams do not like to have their hearts broke, let them avoid Henry'" (Chapman I:4, 42-3).
This foreshadows the plot to come. It also hits Mary's presentation of herself as gay, insouciant.
Then there is his curious response to Mrs Grant's disbelief:
"'My dear brother, I will not believe this of you.'
I wonder in what tone the others read this? Is it insinuating? How heavy does one make the voice? Is it lightly ironic throughout with a smile or only at the close with a final drawl? Depending on how you read these lines depends how you will "read" Henry. His lines are capable of different readings.
Mary leads us to think he is laughing at Mrs Grant and refers us to Milton's slightly anti-feminist line for Eve:
"'There, Mrs Grant, you see how he dwells on one word, and only look at his smile. I assure you heis very detestable--the admiral's lessons have quite spoiled him' (Chapman II:4, 43).
Mary of course finds this anything but detestable. It amuses her.
The second dialogue is less enigmatic. Henry does mock Mrs Grant: 'Oh! yes I like Julia best,'" but is driven from mockery by their insistence he answer them which he likes best, by suggesting he likes an engaged woman. He says it is safe. Austen perhaps wants us to see how he will use and play with a woman. On a second read of the book though one thinks, he laughs last who laughs best. And "says who?"
Mary too comes across as mocking, harder, and disillusioned. She also plays the world's game and begins when Henry's hint that perhaps she thinks Maria is not "safe," that that "it is a great match for her." Henry will not let her pass and says he knows she thinks that Maria Bertram is going to marry a man whom she "does not care three straws for." He of course does "not subscribe to this." He "thinks too well of Miss Bertram to suppose she would ever give her hand witout her heart."
The ironies are many-sided--as well as what I'll call the bitchiness (men can be very bitchy too). Mrs Grant and Mary are amused. But this brings out Mary's views on marriage itself. It is a taking in: "there is not one in a hundred of either sex, who is not taken in when they marry" Mary says it is all playacting, hypocrisy, and self-delusion. Mrs Grant denies it, and says one can find "comfort somewhere" but this is something a bleak response if you think about it, and Mary does not really accept it:
"'Well done, sister! I honour your espirt du corps. When I am a wife, I mean to be just as staunch myself; and I wish my friends in general would be so too. It would save me many a heart-ache."
Now this is said with a light drawl, ironically, and is a piece with her ability to appear to accept Maria's marriage at face value. We know it is because of Mrs Grant's response: ""'You are as bad as your brother, Mary; but we will cure you both. Mansfield shall cure you both--and without any taking in'" (Chapman II:5, 45-7).
Certainly no-one at Mansfield tries to take this pair in. They couldn't.