First of all your grandfather's property shall devolve equally among all his 10 children.
The daughter also have equal rights hence if someone stakes claim towards their legitimate share, then the so called oral partition among four sons alone will not be valid in law.
Now coming to the alienation part, if other brothers dont have objection to this, then the person who sold this may have taken it for granted.
In any case, if the property was allotted to him, he need not take anyone's permission for that, he may feel that he need not answer to someone's sentimental attachment to the properties.
You may consult a local advocate on further issues.