Liability of us citizen in indian property

You are asking trick quetion. You are sayinng all assessts in your name as well as you are saying as per Will you and your brother have 50% share each in property. However, if there is Will and your brother is having knowledge of Will and may have copy of it. Then, he can claim his 50% share. Nationality doesn't effect rights created under Indian law. You and your brother has equal rights. As well as since he is your brother i.e. one of his parents may belong from Indian origin, so he have Indian citizenship as well. Still doesn't change anything. 

Thanks for your reply Shrey.

Also, is an unregistered will valid ??

Yes. Unregistered Will is valid but there are some exceptions. It has to pass its credibility test. Such as before whom it was written i.e. Witness and It should not be forged one. If it is written by person who made his will then that's good. 

Please post the complete facts and the real issue(s) instead of posing riddles.