Property Purchase

Property from my father which is around 2400sqft in bangalore. Iam the only daughter to my father and i have 3 elder brothers and the property was divided into four parts and one of the part belongs to me which is around 600sqft but due to personal concerns we planned to extend our property by purchasing one of my elder brothers property but unfortunately he is dead and no more with us. but as per law his wife is alive and she is in good state of mind and now the property is also registered on here name and now my question is : 1) if i purchase the property from here is it compulsory or mandate to have all here sons and daughters present while registration. 2) The lady from whom iam purchasing the property has lost one of here son and that son had two wife's, one wife without children and one wife with 5 childrens should i get all of them to registrars office during registration. If any of my brother or sister could guide me on this i will pray for them my entire because i dnt want to get into illegal stuff.