Self acquired property

As per your concern let me tell you that mere regretting the transfer of property is simply not a solid legal ground that could be used to retransfer the property to your name now.
Currently, the father-in-law needs to move to a court of law that has competent jurisdiction over the matter and should file a suit for cancellation of the instrument on the grounds of illegal i.e. basically stating that it is vitiated by coercion.

However, the coercion would be required to be proved through cogent evidence. In addition to this, before the retransfer is complete the legal heirs of the father in law will have no rights over the property.

Hope It Helps!

Regards,
Kevin M. Paul