Senior citizen harassment

My grand father(mother's father) is approx 70 year old and he has two daughters. His younger daughter is now 45 year old that couole doesn't have children. They have tried for IVF several times and it didn't succeeded. There was small family quarrel between my grand pa his younger son in law and since that time he is not even sending her to regularly visit her father. But whenever they need some money they are harassing my grand pa in the name trying for IVF again at the age of 45 to her. They even asked my grand pa to distribute assests in two parts now itslef and they want their part to be transferred. We are not saying yes for that because he is single and we are asking them abt his livelihood, so we are asking to split it in three parts in that case and after his death third part will be distribited between the sisters. They are not ready for that and recklessly saying they areleast bothered about his livelihood and health. I just want to know how can we give a peace of mind to my grand father by approaching legal department to put his younger daughter and son in law away from him from these kind of harassment. And his younger son in law is a government servant, but he is still doing this kind of harassment without any fear. We are bearing all these from almost 15 years and we are not in a position to bear all yhese for the good of my grand pa's health and his peaceful livelihood. So, i need help in this matter to approach the correct aithorities.