To be fair Carvajal is alread old, so whoever their next "los galacticos" move will be, it has to be a right back, and there are a lot of talks about Trent Alexander Arnold will end up at Real Madrid this summer, he still hasn't signed back with Liverpool, so it could be done. I am not saying its done, because we have no news yet, TAA is still free agent this summer by how its going, he can sign back with Liverpool too, or he could just go there. VVD is also getting free, but he is 33 years old and won't help Real Madrid much, so they need to find a good defender, a center back, to get to that position. They need to focus a bit more on their defense, that would help them a lot more.
Real Madrid is very serious about signing Trent Alexander Arnold and I believe the player is going to come to Real Madrid because many signs show that the player wants Real Madrid, the player has not shown interest in signing a new contract with Liverpool and that gives Real Madrid full confidence that they can get the player, Real Madrid will sign Trent Alexander Arnold next season as both teams have a good relationship with each other.
About Virgil Van Dijk I don't think Real Madrid will want to sign him, from the player action if Real Madrid wants to sign him he will accept the offer because the player has a good relationship with Rudiger and he will want to be Rudiger's partner and become best defenders in La Liga but Real Madrid want a young defensive player, Real Madrid is planning a good signing next season that is why they don't want to sign any player in January transfer market.