Who are Pitru Devatas? Is Pitru Dosha caused due to the Pitru Devatas being unhappy? How many generations of ancestors are counted as Pitru Devatas?
There are two categories of Pitṛs - the Manushya Pitṛs and the Deva Pitṛs. The Manushya Pitṛs are our ancestors departed to the other loka and the question of generations arises when we talk of them. In the case of Deva Pitṛs there’s no concept of generation as such. The Deva Pitṛs are described below.
The Pitṛs are said to be of seven classes, variously descended from the seven sons of Brahma as per the Manusmriti 3.201 (view endorsed by Brahmanda Purāṇa Upodghata Pada 1.48-49) of which 4 have embodied forms and 3 do not. The three that do not, live in heaven and are described in the Manusmriti 3.195-196:
The Somasads, the sons of Virāj, have been declared to be the Pitṛs of the Sādhyas; and the Agnisvāttas, the sons of Marīci, are famed in the world as the Pitṛs of the Gods.—(195)
The Barhisads, the sons of Atri, are declared to be the Pitṛs of Daityas, Dānavas, Yakṣas, Gandharvas, Uragas, Rākṣasas, Suparṇas and Kinnaras.—(196)
The Mahabharata 2.11 calls them as Vairajas (sons of Viraj), Agnisvāttas and Garhapatyas respectively.
These 3 together with Yama, Aryama, Kavyavaha and Soma are called the Divyapitṛs:
कव्यवाहस्तथा सोमो यमश्चैवार्य्यमा तथा॥ अग्निष्वात्ता बर्हिषदः सोमपाः पितृदेवताः॥84.12॥
Garuda Purana Acharakanda
- Yama needs no explanation. (He is the king of the Pitrs as per Brahmanda Purāṇa Upodghata Pada 1.52)
- Soma: the moon and giver of Soma to the Pitṛs as per the Matsya Purana Chapter 141.3 - सोमाच्चैवामृतप्राप्तिः पितॄणां तर्पणां तथा।(The Shukla Yajurveda 16.58 mantra for tarpana calls the Pitṛs as drinkers of Soma)
- Aryama: he is one of the sons of Aditi as I discuss in this question
- Kavyavaha: he is one of the 49 Agnis. As per the Vayu Purana, he is the grandson of Agni and son of Pavamana. The Purana describes him as the Agni of Pitṛs, which gives the Kavya or offering to them (in the Pindapitryajna or Pindadanam) :
देवानां हव्यवाहोऽग्निः पितॄणां कव्यवाहनः।
-Brahmanda Purana Anuṣaṅga pāda, 12.5
When doing Divyapitṛ tarpana, the above seven are invoked.
For pitru dosha it’s more from manushya pitṛs. You can get a fair idea from: