I feel like Kylian Mbappe would be on the left wing, Endrick as the center forward and Vinicius Junior on the right wing.
You are saying Endrick will be in the starting eleven quickly? Honestly I don't feel like that man.

Ancelotti prefers to keep this kind of young talents on the bench for a while and asks from them to be patient for their time. The same thing happened to Vinicius Junior also and it is happening to the new young talent Arda Güler as well.
This is why I'm expecting Mbappe to be at the centre, Vinicius Junior on the left wing. For the right wing, Rodrygo/Valverde can be preferred. However this is valid if Ancelotti prefers 4-3-3 formation.
If we see a formation with 2 strikers, Vinicius Junior - Mbappe duo might be seen and Bellingham right behind them.

These are just predictions of mine though so let's see...
We don't yet know the exact formation that Ancelotti will use next season, but if you look at the player material he has, Ancelotti has several options. Ancelotti preferred formation is 4-3-3, but last season Ancelotti experimented quite often with various formations, depending on the opponent they were facing. I think next season Ancelotti will do the same thing, to be able to give each of his players decent playing minutes, so that no potential is neglected. The addition of Mbappe and Endrick will certainly make Madrid front line competition even tighter, but for Ancelotti this is a blessing.
As a manager, Ancelotti would certainly be very happy if Madrid management could bring in quality players Mbappe and Endrick in the transfer window, this would make Ancelotti task easier. With the convenience he has, Ancelotti has the opportunity to present various trophies every season. Meanwhile, Ancelotti will most likely prioritize experienced players, and Endrick will be plotted as a second tier player. With the many competitions that Madrid will participate in next season, Ancelotti can rotate every available player.