Sri Sri Guru-Gaurangau Jayatah
Respected Guru Maharaja and all devotees,
Srimad Guru-caranebhyo Namo Namah
Srimad Vaisnavebhyo Namo Namah
Srila Prabhupada-kiritr Vijayatetaram !
For the pleasure of Sri Hari-Guru-Vaisnavas and for my own purification, let me share my understanding on this:
Dear Gilbert ji, Please accept my humble obeisances.
Regarding praying for the sick, Srila Prabhupada introduced the chanting of the Nrsimha prayers specifically for his disciples to petition to Nrsimhadeva to protect Srila Prabhupada.
Regarding transferring results of chanting to others, there are precedents for transferring pious results (of any pious or spiritual activity/thing like tirtham) to others (as seen in Gita-mahatmya found in Padma-purana) but it has not been widely practiced among Vaisnavas. Hari-Bhakti-Vilasa 11.271 onwards does mention chanting various names of Lord Vishnu (just like Vishnu-sahasra-nama) for particular material desires, however, that is for those whose mind has been afflicted with material desires. Please note the following:

Sadachara-pramana neither promotes it nor prohibits this practice. So, it's up to individuals to exercise their will in this regard. However, the vidhi of transferring one's pious credits to someone should be properly known. To me, it appears that simply uttering 'sankalpa' for chanting any Vishnu-names for any particular purpose is sufficient for this. The exact vidhi can be learned from traditional purohitas.
Regarding the departed souls, it is understood that by the devotional service of the devotee, his deceased relatives are also benefited. Traditionally only sraddha is done for the dead and that is considered sufficient.
Hope this act of mine pleases Sri Hari-Guru-Vaishnavas,
dasabhasa, jay nityananda das.