Sale of non agricultural land is a business income or capital gains income?

Owner of property :Late s.janaki

After demise of Mrs. S.Janaki on 21/08/2016, The property Came to the possession of her legal heirs (i.e., Her husband and sons).
They gave general power of attorney to Mr. D. Jhon who is authorized to develop and sell the property on behalf of the principals. Mr. D. Jhon General power agent along with his property has developed and obtained layout, DCTP approval.

In this case sale of such land araise the income is treated as business income or capital gains income in hands of legal heirs?