1 it is not clear what sort of deed is executed in favour of the son.
2. it is not clear how the same ws done in favour of the son when his father already died by that time.
3. If the property owner during his lifetime made any registered deed of conveyance like gift deed in favour of his son then only he can sell the same to you now.
4. otherwise all his siblings have equal undivided share in it and this man alone can not sell the property.
Do get the title deeds checked by a local advocate.