And with Alisson, in contrast, I would sit down and say something like this: "We think you are a great guy. And you've already proven yourself to be a legendary goalkeeper here. We would like you to be part of our club in some capacity even as your playing career starts inevitably slowing down. We don't see those things as matters of money. You are a great guy and you obviously also have great value as one of the world's very top modern goalkeepers. What do you think? You are also a Brazilian. We would be totally fine with you being associated with us and with some club/institution in Brazil too. We suppose you would probably want and like to have some sort of a professional link with your home country." That is for Alisson.
And for Trent, VVD and Salah let the contracts expire with Trent being let go in January as the optimal outcome. It is very best for Trent's own sake for him to leave too. And VVD and Salah know that their careers will go down when they leave Liverpool. They will have options at the end of the season but those will be downward options for them. They might take them or they might not. Those are things that can be negotiated. That's what's done when players refuse to negotiate at the more appropriate time and decide to start blackmailing the club. That stuff must be rooted and stamped out because otherwise such things become the norm.
And then give more careful thoughts in the future to what sort of personality profile is given the captaincy. And is allowed to boss other players around in the dressing room, on the training pitch, etc. Steven Gerrard was a good captain. It is always good to have a local lad that happens to deserve the captaincy. But those things can be rare. Not everyone can captain the team. Steven Gerrard also wanted to leave the club at one point. He almost signed for Chelsea. He was seeking a place where he could win more titles. His head was turned. But in the process of thinking about and doing such things he didn't and he wasn't blackmailing the club.
Once Alisson is approached as I described above, if he responds by saying "I can get more money in other places" then he can be told "Yes. We understand that. There is more money you can make elsewhere. But we don't see this as just matters of money. Of course that you are free to do that. We will pay you decently but we are not going to compete with whoever out there is willing to pay however much they happen to be willing to pay to get you out of this organization."
ps And if he, f o r . . e x a m p l e , makes media statements after consulting with his agent about how he wants to be a team captain in the future to rile up the supporters and sell himself to other clubs, or aaaaaaaaaaanything like that, then we just don't deal with such players. They can find the door themselves.