The Law Code of Yājñavalkya 1.10.46

1.10.46

daive ābhyudayike śrāddhe yugmān samān brāhmaṇān upaveśayet | katham yathāśakti śaktim anatikramya | tatra vaiśvadeve dvau mātrādīnāṃ tisṛṇām ekaikasyā dvau dvau tisṛṇāṃ vā dvau | evaṃ pitrādīnām ekaikasya dvau dvau trayāṇāṃ vā dvau | evaṃ mātāmahādīnāṃ ca vargatraye vaiśvadevaṃ pṛthak tantraṃ vā | pitrye pārvaṇaśrāddhe ayugmān viṣamān upaveśayed iti saṃbadhyate | etac ca paristṛte sarvataḥ pracchādite śucau gomayādinopalipte dakṣiṇāpravaṇe dakṣiṇato 'vanate deśe kāryam || 1.227 ||

In the divine rite, that is, in an auspicious ancestral rite (ābhyudayika-śrāddha), he should seat an even, equal number of Brahmins. How? "According to ability," without exceeding one's capacity. There, two for the Viśvedevas; two for each of the three [female ancestors], namely the mother and others, or two for all three collectively; similarly, two for each of the father and others, or two for the three collectively; likewise, for the maternal grandfather and others; and for the three sets [of ancestors], the divine offering to all gods (vaiśvadeva) may be performed separately or jointly (tantra). "He should seat an odd number for the ancestral" is the construction, meaning an uneven number in a regular ancestral rite on a new moon day (pārvaṇaśrāddha). And this must be performed in an enclosed spot, covered on all sides, clean, smeared with cow-dung and the like, and sloping toward the south, inclined toward the southern direction. // 1.227