Do you have the title deed in your name? If yes, then you need not worry. The ownership is transferred in your name, so legally it is yours. Also, when someone buys a property, a PUBLIC NOTICE ad is posted in newspapers where it is notified that said property is being sold to "X" person. If anyone has any objection, they can approach "X". This works as a no objection.
So, unless it is an Ancestral property and there has been some kind of misrepresentation to you while selling it, you do not need to take a NOC from those legal heirs.
Let us know if you have any further queries.