Does new will revokes old will if first will was registered

Please let me know the following (1) if a person has a will which has been registered earlier and later after 3 year he prepares a new will in which he revokes all his previous wills and has notarized same which will would be considered as valid?(2) Can a person transfer all his property to his children rather than his surviving legal wife without her concern/knowledge? Can the wife challenge such will as she has give her 50 years for the same family? (3) Incase if in the will the person has transferred his property to first and second children out of 3 children can the 3rd child challenge