Vaishnava Dharmashastra 18.14

18.14

atha brāhmaṇasya brāhmaṇavaiśyau, tadā ṣaḍdhā vibhaktasya caturo 'ṃśān brāhmaṇas tv ādadyāt ||

Again, if there are two sons of a Brâhmana, and the one belongs to the Brâhmana and the other to the Vaisya caste, the estate shall be divided into six parts; and of these, the Brâhmana shall take four parts;