Is it permissible for a person to offer the funeral prayer (Salat al-Janazah) for their parents who passed away a long time ago, if they were not religiously observant at the time of their death and they doubt whether the funeral prayer was performed for them in their village?

The questioner's doubt about the funeral prayer for his parents is unfounded, because the original principle is that Muslims pray over their dead before burial. As for his praying over them after the appropriate time has passed, scholars have differed regarding praying over the grave and its duration. Some limited it to a month, others to a year, and some permitted it as long as the deceased's body has not decayed. If the questioner doubts the decay of the body, he may pray over them. However, it is more proper for him to strive in supplicating for them, for the supplication of a righteous child benefits them.