The text in chap 16 does not say the Woodhouses were second in wealth to Mr K, but that they were second in consequence. The Woodhouses may be richer, but the landed estate of Hartfield was small -- "being but a sort of notch in the Donwell Abbey estate, to which all the rest of Highbury belonged; but their fortune, from other sources, was such as to make them scarcely secondary to Donwell Abbey itself, in every other kind of consequence;".

The Woodhouses were cash rich but land poor, while Mr K was cash poor but land rich, and in their society being land rich gave greater consequence than being cash rich.

I don't think Mr K needed to help his brother, very likely John would have inherited some money to set up his practice (although the landed estate was inherited by the elder brother, it did not mean that younger brother was penniless and inherited nothing, he probably got cash, maybe that was why Mr K had not much cash). John K was a "very clever man, rising in his profession",(chap 11), he could be making money and might rise to the top of his profession and later be appointed as a Judge and take precedence over his elder brother (like Darcy's great uncle the Judge, who must have been his grandfather's younger brother).