The Central Government Rule says that there is no bar for Governments servants to join purely artistic, literary, scientific or charitable organizations,which are not a source of profit. But if your brother's superior officer asks him not to be associated, he will have to refrain from. It will be an uphill task to get clearance again. But if the order of the superior officer does not come within reasonable time no action can be taken against your brother.
I have checked the Rules of a few State Governments. They are also a repetition of same Rule only.