No need to lock him down this winter already, the priority was lock one of them down, then we have until the summer to get/convince the other one to join us too. And since we got one of them now, that should give us a nice advantage ahead of any other clubs, not to mention Barca was De Ligt and De Jong's first choice either way anyway.
If our Board will stop messing around and let Ajax and especially De Ligt know that we're serious about getting him, and keep in touch with both parties throughout the next few months, i don't see us losing out on him in the end. And i really hope we do get him, getting De Jong was already a major coup, but also getting De Ligt would just be a massive statement of intent, that we really have the best sporting project for the next 10 years, and that we're already almost ready for life after Messi. Until then, he's just a bonus on getting great players to join us, because they want to experience playing with the GOAT, until they can.
Imagine MATS, De Ligt, Umtiti, De Jong, Arthur, Alena, Puig?, Oriol?, Dembele, Coutinho?, Malcom?, now that's a healthy core of players for the next decade. Now obviously we won't keep all of them, but even if keep only the major ones in MATS, De Ligt, Umtiti, De Jong, Arthur and Dembele, we should have a strong core to build on even years after Messi retires.