Garuḍa Purāṇa 21

Garuḍa seeks clarification from the Lord on the following: Suppose the mother of a man dies when his father, grandfather, great grandfather and great great grandfather along with their wives continue to live, with whom his mother would be joined on the day sapiṇḍīkaraṇa by means of sapiṇḍana? She is joined with Umā Lakṣmī and Sāvitrī, the three Goddesses. However, this is the rarest of the rare cases.  On the day of sapiṇḍīkaraṇa, the preta body of the deceased is given a place in the world of ancestors. Thus the preta body of the dead becomes a pitṛ. Ancestors are classified into three categories – father is called Vasu, grandfather is called Rudra and great grandfather is called Āditya. His mother is classified with their wives. A woman is not connected to her family lineage after marriage and her lineage gets transferred to her husband’s lineage.  The following example can explain this further.
Before father’s death
great grandfather
great great grandfather*
After father’s death
great grandfather
(*great great grandfather becomes tyājaka@)
@ Tyājaka  means the one who abandons.

When a deceased person leaves the world of Āditya, no further piṇḍa is offered during annual ancestral rites known as śrāddha rites are performed. Generally, while calculating generations, twenty one generations are taken into account, ten past generations and ten future generations taking the performer as the middle point (10 + 1 + 10 = 21).

When śrāddha rites are performed, the performer and his family are blessed by his ancestors. His father blesses him with sons; grandfather and great grandfather bless him with wealth. It is also said that a corpse should not be cremated when the following stars are in conjunction with the moon - Dhaniṣṭha, Śatabhiṣā, Pūrvabhādrapada, Uttarabhādrapadā and Revatī. If necessity arises, certain remedial measures are prescribed such as making an effigy out of darbha grass and burning it before cremating the body.

There are sixteen śrāddha rites prescribed and they are at the place of death, midway to the cremation ground, at the pyre, in the hand of the corpse, one at the cremation ground, one at the time of collection of bones, and the rest ten during the first ten days from the date of death.  The reckoning of this sixteen is said to be appropriate.  If this is done, monthly rituals need not be performed. 

The hands of the corpse should be tied together and the big toes should also be tied together and the corpse should be covered with a white cloth. The corpse should be placed on bamboo logs. If a corpse is taken out in the night, evil spirits could attack the corpse. But as such, there is no prohibition for cremating in the night. A corpse should never remain unattended.  Someone should always be present with the corpse till it is burnt.  The corpse should not be touched. In the presence of a corpse, no one should take food or even drink water. All other ceremonies should be postponed including other śrāddha rites and worshipping gods. Temples remain closed.  This is the kind of respect that is being paid to the corpse.

The Lord provides certain additional details. If one dies due to fasting, he merges into the Brahman.  If one dies after resorting to sanyās, it is equivalent to dying due to fasting. If a person resorts to fasting when he is affected with serious disease, he is also not reborn. If a sick person, knowing that he is going to die resorts to sanyās, he is also not reborn. Frequent visits to holy places wash off sins.  It is has been repeatedly emphasized that one should make as many gifts as possible during his life time.  However, gifts should never be given by resorting to borrowing.

{Further reading:  While performing last rites, one should never borrow money and complete the last rites.  Last rites should be performed only within one’s means.  No gifts should be made by borrowing money.  Such gifts not only dissatisfy the dead but also cause the accrual of sins for the performer of the rites. If one has enough wealth, then all the gifts discussed earlier should be given and ceremonial rites should be performed in a grand manner by providing food to the needy.}