Bellingham is actually suitable to be the team captain because he has a leadership character and can encourage the team when they are frustrated or whatever. But we all know that Real Madrid always has a tradition in having a team captain, they prioritize senior players, players who have served the club for a long time who become captains and so on down the line until whenever in Madrid. They are not another club where new players can become team captains.
So Real Madrid with the tradition of choosing a captain, of course the next captain is those who are senior and those whose deputies are below them. Like in the era of Hierro, Raul, Casillas, Ramos, Marcelo, Benzema, Nacho, and now Calvajar and after that Modrick, Lucas Vazquez. So if you look at the tradition, Bellingham and Mbappe still need a long time to become captains at Real Madrid.
Real Madrid has many leaders who can be captains, but here you also need to take into account the player's experience. But I don't think it's a big problem to choose a captain in the team and this can be done by the coach, whose choice cannot be disputed. Real Madrid still has two matches with not the most difficult opponents, so I think that they will even try to rise higher, I don't know about the top 8, but they will definitely make it to the playoffs.