Selling De Jong and Lewandowski is not a bad idea, these two players still have a high selling value, especially De Jong, who has attracted the interest of several elite European clubs. The money obtained can be used to bring in William and indirectly the club's expenses will be reduced because these two players have higher salaries than other players. Barcelona can still rely on Vitor Roque as a replacement for Lewandowski, while in De Jong's position there is no need to worry because they still have several quality midfielders.
That might be a wise enough option for Barcelona, but is the Barcelona team thinking about that now? Because if this is what the Barcelona team is thinking about, of course they themselves will never remain silent and will immediately move to make this happen. But if Barcelona can bring in William without having to sell these two players, I think this option is also very good because experienced players like De Jong and Lewandowski can still be relied on by Barcelona next season with different levels of quality.