father can execute sale deed for transfer of assets and liabilities of sole proprietary concern by father in name of 2 sons. There are other ways such as simthshah said is by converting it into LLP. Another way is by executing the gift deed and transfer all the capital to his two sons as a gift but the only catch is, the gift deeds are very hard to be transferred.

Source: https://www.kaanoon.com/83333/transfer-of-proprietorship-partnership-from-father-to-sons