how to protect from illegal selling ofjointly owned property

you need to advice through local advocate to file the case refraining your bother to do so.

but firstly send and legal notice cum intimation in all local newspapers that you are the joint owner of the property and not interested in selling such property in case of any querry to visit or meet local advocate so & so.

The purchaser cannot get a good title if he purchases the joint property without your signature. If you feel necessary then issue notice to your brother not to sell the property without your permission and also publish the matter in the local daily for safety.