The presence of Rudiger can already complete the Real Madrid defense. Militao doesn't look very strong, but next season he will be starting to mature and is very suitable for a duet with Rudiger.
When Rudiger was young, he played as a right swing back and he did it well but now he is old and is not good for that position. Alaba is no longer young too. I think Alaba and Rudiger will play in central of Real Madrid defense system. Militao will be substitution for them or he can play at right or left side.
Alaba could have been returned to his original position at left back.
I don't think Alaba will feel happy with this change because of his age. He can play in many position but his best position for now, in my opinion is central area, in defense system or midfield.
Tchouameni is Real Madrid's main target to regenerate the midfield, because in this position many players have started to age. Real Madrid also release a lot of old players, so it is imperative for them to find replacements to add depth to the squad. Maybe for the next season, Ancelotti can still rely on the existing squad.
I can not say too much about Tchouameni but if he is a strong defense midfielder, it is a good deal for Real Madrid to support Casemiro now and replace Casemiro in future. Camavinga is better with attacking even he can do both but it seems Real Madrid will use him at his best with more freedom to do attacking, than support defense in midfield.