Oh that all seems to have a mountain Farage was trying to make out of a molehill by the way. It seems like he simply didn't qualify for the type of bank account he had, so the bank wanted to transfer him to a different type of account and he refused, leading to his account simply being closed.
Ironically, reading between the lines it may be that he was using his personal account as a 'family' one which his kids could also withdraw money from. But that became a problem as they're not British residents so, post-Brexit, money keeping on being taken out of the account from within the EU became an issue for the bank. But like I say, it seems like he was simply offered a move to a type of account he could use for that sort of transaction and refused.
So, really, this is just one of those misplaced consumer complaints via social media that's writ larger, and stupider, than most.
(Meanwhile, whether there are tax implications for any income from their father that his grown up children haven't been declaring will be a matter for, I'm guessing, the German equivalent of inland revenue.)