Theoretically the shastras provide a provision to give power of attorney to a brahmana to do pinda pradana on behalf of others. This is followed when a childless widow wants to perform the rites for her husband and in similar situation. The only catch is that the Brahmana must lead a "Brahmana life" - i.e. he should stay without food the previous night; not have sex the previous night; should not eat outside home; and must not eat anything till he offers pitr tarpana. If you can locate any such person [even in India], then you can ask the gentleman to do pinda pradhana to your wife on behalf of your family.
However, please note that this is not an alternative to your son doing whatever he is doing. It is an additional exercise to satisfy your feelings.
As per Garuda Purana, what your son is doing is also allowed. I am not sure if you are offering any dhana to a Brahmin. It is mandatory to give rice, dal, salt, jaggery, coconut etc along with some dakshine to a Brahmin in your area before you eat lunch that day.
Puranas state that the pitr must be invoked within the Brahmana and he should be fed that day. For our own reasons we seldom do that even in India. While offering the food articles, you invoke the spirit of the person within that Brahmana and ask them to accept these offerings.
You can pay some money that day for brahmin feeding in either Kanchi / Sringeri peetham, ISCKON Temple in Bangalore or in some Raghavendra Swamy temple in India. It will cost you $3 to feed a Brahmin. It is called as Hasthodaka Seva. I am aware that you can do online booking of hasthodaka in Mantralayam that day [
https://srsmatha.org/daily-seva.php]