Re: Tharpanam while parents are alive
Yes the month of Bhadra Krishnapaksh (dark fortnight) begins the time allocated for ancestors. The first Shradh according to calendar I follow begins on Tuesday.
This tradition of Tarpan is an age old tradition offering the oblation to the departed soul. Even Lord Ram upon hearing the death of his father immediately entered the river to do the tarpan. In Bhagvat Gita Arjun was also perturbed and concerned;
kula-ghnanam kulasya ca
patanti pitaro hy esam
This brings the family and the slayers of the family to hell, because the spirits of their ancestors are degraded when deprived of ceremonial offerings of rice-ball and water.
There is no reason why you can't offer oblation to your ancestors, the last day of Shradh is allocated to serva (all) Pitra
Jai Shree Krishna
Rig Veda list only 33 devas, they are all propitiated, worthy off our worship, all other names of gods are derivative from this 33 originals,
Bhagvat Gita; Shree Krishna says Chapter 3.11 devan bhavayatanena te deva bhavayantu vah parasparam bhavayantah sreyah param avapsyatha Chapter 17.4 yajante sattvika devan yaksa-raksamsi rajasah pretan bhuta-ganams canye yajante tamasa janah
The world disappears in him. He is the peaceful, the good, the one without a second.