Ancestral property gifted from grandfather to grandson revocable?

My Grandfather gifted land property to me and my brother and registration has been done properly.. but property is ancestral property My grandfather still alive and he don't want to wish to give property to my other cousins which father(My uncle) and one cousins mother already died in 2009.. They are challenged my grandfather in court about ancestral property gift out of law..then ..Is a property gifted revocable?