The Law Code of Yājñavalkya 1.10.49

1.10.49

daive vaiśvadeve dvau brāhmaṇau prāṅmukhāv upaveśyau | pitrye ayugmān ity aviśeṣaprasaṅge viśeṣa ucyate trayaḥ pitrye iti | pitrye pitrādisthāne traya udaṅmukhā upaveśyāḥ | pakṣāntaram āha ekaikam eva vā | vaiśvadeve pitrye ca ekam ekam upaveśayet | saṃbhavato vikalpaḥ | mātāmahānām apy evaṃ śrāddhe nimantraṇādi | dvau daive prāk trayaḥ pitrye udag ekaikam eva vā ity eva mataṃ pitṛśrāddhavat kartavyam | pitṛśrāddhaṃ mātāmahaśrāddhe ca vaiśvadevikaṃ pṛthak tantreṇa vā kartavyam | tantraśabdaḥ samudāyavācakaḥ | yadā tu dvāv eva brāhmaṇau labdhau tadā vaiśvadeve pātraṃ prakalpya ubhayatraikaikaṃ brāhmaṇaṃ niyuñjyāt | yathāha vasiṣṭhaḥ |

In the divine rite, for the Viśvedevas, two Brahmins should be seated facing east. Since "an odd number for the ancestral" would be too general, a specification is stated: "three in the ancestral." In the ancestral rite, in the place of the father and others, three should be seated facing north. He states an alternative view: "or one for each." He may seat one for the Viśvedevas and one for the ancestors. This is an optional alternative according to possibility. The invitation and other steps are the same for the maternal grandfathers' ancestral rite as well. Thus the view that two facing east in the divine, three facing north in the ancestral, or one for each, should be performed just like the ancestral rite for the paternal line. And in the rite for the paternal ancestors and in that for the maternal grandfathers, the offering to all gods may be performed separately or by a single combined procedure (tantra). The word tantra signifies a common collective performance. When, however, only two Brahmins are obtained, he should assign a plate for the Viśvedevas and employ one Brahmin for each of the two [sets of ancestors]. As Vasiṣṭha says: