Regarding three settlement deeds

1) I have read in one of the settlement deed registration that when a senior citizen executes a deed a doctors wittness is essential sir please let me know such related judgements and also the act 2007. My father a senior citizen of Indian Airforce aged 89 yrs he had brain stroke, Heart problem,Hypertension, liver problem etc in the yrs 2006,2008,2009 We are 6 childrens My 4th brother fraudently registered coluded with registrar all the properties in his minor childrens name and he as there guardian (three settlement deeds total 33 pages each pages he obtained signature as well as thumb imperssion beside the signatures The thumb imperission affixed by the side of the signature in the documents gives a doubt as to why it was affixed when there is a signature in each page. My father is a well educated person. In the settlement deed it is mentioned after my demises. kindly let us know whether it is a WILL or SETTLEMENT. On27.11.2010 he was admitted for brain stroke my brother discharged him on 29.11.2010 and the documents were executed on 3.12.2010 without informing us. within 3 days he registered the documents. The witnesses in the document are chance witnesses and are not known witnesses. As per doctor report my father had a brain stroke several times mentioned by doctors as brain ischemia and aphasia, CVA How can I prove it we already filed a suit in the District Munsif court,Tambaram