I read that too, that Charles doesn't love Balmoral castle as much as the Queen did, though he loves his little property on the grounds there, where he is staying currently. But, there might be some push back from other family members who are used to having Balmoral for weekend visits and such. I'd say they are likely out of luck and are going to have some of their luxuries and privileges cut back. If he wants to reduce costs, turning it into a museum would make sense. I'd go to Balmoral, pay the fee, and do the tour.
I've read too that he has a number of properties that he'll have to decide what to do with including Highgrove.