The phrase `north of England' would have been taken by her readers at the time to mean that the Bingley fortune was made in the Industrial Revolution in the rapidly industrialising north -- wool, cotton, iron, etc.; there's no reason to introduce Mr Bingley's grandfather here, as a father would suffice.

Fotunes could be made so quickly that it was perfectly possible that Mr Bingley's father, starting out `respectable' (ie not poor, but of the middle ranks of society) could have accumulated enough in his life to send his son to a posh school (where he might have met Mr Darcy), and his daughters off to an expensive private seminary; towards the end of his life, he'd have looked to buy a landed estate and retire.

The Bingley sisters are `in the habit of spending more than they ought': ie they're starting to dissipate the fortune. `Clogs to clogs in three generations' was said about fortunes made in the Industrial Revolution: one person made the fortune, his son maintained it, and his grandchildren squandered it. I don't know whether JA heard the saying, but I reckon she'd agree with it.