when a muslim dies we can pray for him , (for example his/her sins to be forgiven). But in case of a non muslim we cannot do anything or even express sorrow this is what I heard. I want to know, how did the prophets behave when their loved ones in disbelievers died? How did they express their grief or mourn?
Before the Surah Al-Munafiqoon (63) verse 7, prophet SAW pray for deliverers, so Allah send down this ayah. After that Prophet SAW never pray for deliverers.
It is all the same for them whether you ask forgiveness for them or do not ask forgiveness for them; never will Allah forgive them. Indeed, Allah does not guide the defiantly disobedient people.
Ask forgiveness for them, [O Muhammad], or do not ask forgiveness for them. If you should ask forgiveness for them seventy times - never will Allah forgive them. That is because they disbelieved in Allah and His Messenger, and Allah does not guide the defiantly disobedient people.
Here 70 time is an example, means, never matter how many times you will ask forgiveness for them, Allah will not forgive them.
As a human being, Muslims are the best, we can join them and share their pain, it is proved by Hadith.