WHETHER "SAHA NAU BHUNAKTU" MEANS EATING TOGETHER?

The  traditional interpretation  is as follows:
The context is with reference to Study of VidyA.

The Sishya prays " Saha nau Bhunaktu." This means " Vidyaphalam bhojayatu" .

The Student prays to the Brahman  to grant the fruit of the vidyA to both the preceptor and himself.

WHETHER PITRU TARPANAM IS TO BE PERFORMED AS PART OF UPAKARMA FOR APASTAMBA SUTRA YAJUR VEDIS?

Based on traditional practice of Sishta BrAhmaNAs, for Yajur Veda Apastamba  sUtra, only KANda Rishi TarpaNam is prescribed. There is no Pitru TarpaNam as part of the  upAkarma ritual.

The upAkarma practices vary in the case of other sUtras . Each one should follow his own sUtra.

For RG Veda  and SAma  Veda, Pitru TarpaNam is there as part of upAkarma ritual.
There are variations in the sUtras. Hence  we have to follow what is ordained in our own sUtra  after properly learning the same from a  Guru.

PROBLEM OF PLENTY IN SANATANA DHARMA

There are many conflicting views floating around as regards the pursuit of dharma whether it is karma kANda, jnAna mArga or Bhakti yoga.
 There is the problem of plenty in sanAtana dharma. There are too many sacred texts, too many paths , too many rituals, too many philosophies, too many AcAryas, too many interpretations that one gets baffled. But life is short and there are compulsions of contemporary livelihood and the force of Kali.
SAstrajNAnam bahu kleSam
citteh calana kAraNam !
It is very difficult to understand and tread the righteous path in the limited time of our existence.
Only the loving grace of the Supreme should guide us.
KrshNam vande jagatgurum !

जयजय श्रीराधे