Answer
(Fatwa: 993/194=H/1429)
It is not necessary for every bad person to go to hell. Also, it is not compulsory that every bad person will live in hell forever. You do not have any doubt about the punishment of hell, rather you suspect about the punishment in grave. It is a kind of mercy for the people deserving punishment of hell that they would be punished first in grave which is a lighter punishment before going suddenly to a heavy punishment i.e. hell.
However, main thing is that it is proved from the Holy Quran, Hadith and books of Aqaaid in detail that some evildoers will get punished in grave.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband