Brother thank you for your questions here a few brief answers inshaAllah full references etc and more in detail information is also available

When we say Ya rasoolalah salalo alyhai wasalam are we asking for help from the prophet salalo alyhai wasalm ?

Help is always sought from Allah Almighty when we say Ya Rasool Allah we are asking the Holy Prophet may salaam be upon him to make dua for us to Allah Almighty

how can he help if he salalo alyhai wasalam help when he has past away?

Because all his passing away means is he slalao alayhai wasalaam is hidden from us not that he is non existent. His bless soul has been returned to him and he salalo alayhai wasalaam is alive in his blessed grave.

Why didnt the Sahabas i.e. Abu bakar, Umar, Ali, Usman ask for help from Mohammed Salao alhai wasalam ?

Who say they didnt? Its nothing but 20th century false propaganda that the blessed companions may Allah be pleased with them did not ask for help through the blessed intercession of the Holy Prophet salalo alayhai wasalaam both during is apparent life and after his passing away

Does the same apply for when we say Ya Ali?

Not the same as Hazrat Ali may Allah be pleased with him is not a Prophet of Allah Almighty, but nevertheless using him as an interceder is allowed


and why cant we say Ya Abu bakar/Umar/Usman etc.

Again who said this? It’s certainly not the belief of the Ahle Sunnat Wal Jamaat


In surat al fatiha Allah says:
You alone do we worship, and You alone do we ask for help.

First the ayah by mentioning worship and help separately shows that these are two different concepts and shouldn’t be thought as one. As far as worship goes we only only only worship Allah Almighty

Second the help referred to in this ayah is the help granted originally, without any need of anyone else; this type of help is only sought from Allah Almighty. However the Quran and Hadith have taught us to seek help via intercession but even when an interceder is used the ultimate help is still from Allah Almighty.