This discussion clarifies the validity of an unregistered and un-notarised Will in India. Generally, a Will is valid if it's signed by the testator and attested by two witnesses, even if written on plain paper. Registration or notarisation is not mandatory for validity, though probate from a court is required for properties located in specific cities like Mumbai, Chennai, Delhi, or Kolkata. If your sister has no objection and the Will meets these signing and attestation requirements, you can proceed with executing it, potentially without probate if the property isn't in a probatable city.