Query On Cancellation Of Property Booking By Joint Applicants

An under-construction flat has been booked by my father and his son in law jointly where my father is the primary applicant. My father has already contributed 50 % of the total saleable value of the flat and his son in law has contributed around 20 % to date. Due to certain disputes in my sister's family (contemplating divorce), my father now intends to withdraw/cancel the booking at his end(and retrieve his share of payment) whereas his son in law is against the plan and wants to purchase the flat by paying the balance amount. My question is: 1. Can the son in law go against my father's wishes and purchase the flat by paying the balance amount and also get the property registered in his own name. 2. In such a scenario, what are the options available to my father to cancel the booking and retrieve his share of payment. Kindly Advise.