At the time of death of father son would be in Sanyasashrama. Now think over how a sanyasi could do Shraddah for the departed Pitrus?
He would have become a Sanyasi after giving up all the worldly desires/aspirations. Family bonds are not sync with a Sanyasi. On becoming a Sanyasi, he is a neither a father nor to son to anybody. Then whither Shraddah here? Further, a sanyasi is always on the move and he is called parivrajak preaching good things. His whereabouts is not known to his son or to others when he dies. The question whether Shraddah was not possible when the father had died while the son was still a householder and not had become either a vanaprasthi or Sanyasi is also irrelevant, since the conduct of Shraddah is itself untenable and unvedic.
