How to handle legal heirs making delay in registration

Dear Sir, Hope subject doesn't sounds completely agreeable with my issue. My father agreed with their father(2 elder daughters & 1 younger son) to register land when he handover balance amount in second instalment. Unexpectedly, he passed away and after couple of days my father paid partial amount from balance amount to his son and had a written statement on stamp duty for received & balance amount. Among them first daughter(lives in India) is ready to register but, other (lives in US) are not ready to register. Whenever we communicate with them they are postponing the dates(as we are asking them to send signed copies with relevant documents) from past 6 months. With all this my father got effected with health issues. Please do help me if we have any alternatives to move forward legally. Am so much gratefully for your valuable advice's.