Hello,
1. If your property is self acquired or otherwise no one can stake claim of any share in it during your life time.
2. You are certainly at liberty to make a WILL and make it favouring any one you desire the property to go to.
3. Neither your daughter in law nor your elder son can claim any rights as you are at total liberty to dispose of the property as you desire.
4. The daughter in law can in no way lay claim on your property in whatsoever manner.
5. Proposed law that gives 50% share in the husband's assets is one that will come into effect in matter of a divorce and as your son does not own any property in his name ,even if the law comes into force it would not have any effect in your case.