I understand that the two Princess Cruises ships, Sun Princess and Sea Princess have been sold. Sun Princess is to become the 'new' Peace Boat ship and they will operate just her. There is no indication to whom Sea Princess has been sold.
I'm surprised that Peace Boat is chartering the Sun Princess, but it does make sense. The organization has chartered the Ocean Dream (ex. Tropicale) from Royal Caribbean's Pullmantur Cruises for 8 years. Earlier this year, they returned her to Pullmantur in exchange for chartering Pullmantur Zenith, but since Pullmantur shut down, the charter is now void so Peace Boat has to return the Zenith to Royal Caribbean. It's obvious that they need a new vessel immediately so that's why they chartered the Sun Princess.
As for Sea Princess, It's still unknown who bought her so we have to wait and see. I suspect the buyer is Seajets because they had also bought her sister ship Oceana and renamed her Queen of the Oceans. Now that none of Sun-class will be sailing for Princess Cruises anymore, this will make the Grand-class the oldest vessels in the Princess Cruises fleet.