I hope , this is not just a hypothetical question put by the member , for entertainment.
Considering it as a genuine concern I would like to respond.
I may approach the matter in different ways.
1)[FONT="] [/FONT]The member’s in-laws are absolutely poor, and their son is reasonably well financially. The in-laws genuinely want to conduct sradha in traditional elaborate way(parvana vidhi).It may entail some expenses ,and the son, who is in the family and who also will get the supposed benefactions of the ritual, is morally bound to contribute for the family ritual.
2)[FONT="] [/FONT] As in above situation, due to some reason ,elaborate prescribed ritual is not possible, due to genuine and unavoidable reasons- then hiranya sradham can be performed.
3)[FONT="] [/FONT]If (god forbid that) the in-laws and son are all financially very strained, then they can perform in whatever way they can—this is only an aapatdharma and not to be used always for an excuse.
4)[FONT="] [/FONT]After all said and done , everything melts down to one’s own faith. The thithis and sradha etc are in vogue to remember one’s parents/forefathers with gratitude at least on that day
I am of the opinion that if one can celebrate , birthdays, wedding days, anniversary of joining in the job, or any other similar thing,(some even celebrate the birthday of their pet dog or cat)-- they are morally bound to give priority to perform the sradha and tharpanam for forefathers as a gratitude for the good things we enjoy in life. As it is not possible to directly interact with the dead, we use symbols--- pitru brahmana,and for (the conductor and pilot)-Viswadeva etc.
If one does not have any belief in all these , he is just free to ignore all these.
(The best person who can be a practical guide in the present case may be the genuine local vadhyar)
Greetings