Thanks @isodoro @traian for the suggestions.
I tried a similar method than the first one suggested by isidoro but my trains got stuck at signals (I must still learn how to place signals correctly)… maybe that was the problem, but is it correct not to place signals just as isidoro did ? Shouldn’t signals be placed on all four tracks entering the junction ?
Is it possilbe to lower a track without demolishing the track itself ? I find it annoying that when you change the track layout or even just electrify the track all the passengers (or cargo) just disappear from stations and trains and that takes a few years to recover.