They have to play together, they look like two players who play for another team and they don't even look like teammates, this will lead them to a breakdown which will then make everything more difficult for Real Madrid, but the coach has to make this clear.
You weren't wrong to say this at Real Madrid start of the season as Vini and Mbappé were playing independently at that time. But look, as Madrid entered the second half of the season, Vini and Mbappé began to develop a partnership, lowering their respective egos, which led to Mbappé becoming La Liga top scorer. One thing that's certain is why their partnership hasn't always been good is that they both occupy the same position. Then, Mbappé was pushed forward as a striker, which isn't easy for a player who is used to playing elsewhere and is given different responsibilities.
What Real Madrid should do now is give Vini a chance with the salary increase he's demanding. If the results are the same, Real Madrid will have to decide to sacrifice one of their players to another team.