The pirate treasure (I think EBD had been reading Enid Blyton) hidden by his ancestor Dai Lloyd was dug up, but Mother Carey and Dickie refused to wear any of the jewellery because it'd been obtained by piracy. The fact that "the Big House" had presumably been bought with the proceeds of piracy was conveniently ignored
In one of her rare admissions that the CS people are not poor at all, EBD says in Oberland
that all the girls going to Welsen, apart from Nita and Nell, were from well-to-do families, and that included Dickie ... although that was after the pirate treasure was found!
The Big House might have been hard to sell in the 1940s, especially as it was in such a remote location. A country pile somewhere might have sold, but the Big House was on a little island: they had to go over to Carnbach even to do basic shopping. He was lucky that he found the School to rent it