By a former marriage, Mr. Henry Dashwood had one son; by his present lady, three daughters. The son, a steady, respectable young man, was amply provided for by the fortune of his mother, which had been large, and half of which devolved on him on his coming of age. By his own marriage, likewise, which happened soon afterwards, he added to his wealth. To him therefore the succession to the Norland estate was not so really important as to his sisters; for their fortune, independent of what might arise to them from their father's inheriting that property, could be but small. Their mother had nothing, and their father only seven thousand pounds in his own disposal; for the remaining moiety of his first wife's fortune was also secured to her child, and he had only a life interest in it.(Ch. 1)

John had already received one half of his mother's fortune when he married Fanny, and was going to receive the rest after his father died; and yes, he was assumed to eventually inherit the Norland estate, which would give him 4000 a year.

Mrs. Ferrars wanted that Edward made a grand marriage, with a woman of rank and fortune.

[Fanny] took the first opportunity of affronting her mother-in-law on the occasion, talking to her so expressively of her brother's great expectations, of Mrs. Ferrars's resolution that both her sons should marry well. (Ch. 4)