How to challenge a registered will

My mother was diabetic for the last 10 years and was on insulin , my father wrote a registered WILL in 2012 before his death favoring 50% share each in my and my mother’s name . My mother was hospitalized atleast 4-5 times during last 2 years and has got her 3 fingers amputated and also had cataract operation , due to her illness she remained aloof and irritable most of the times and during her last days has started accusing my wife of stealing , hiding , destroying , misplacing her house-hold items due to which once they had a small tiff and she went to my grandfather house stayed there for 2 weeks in month of feb and was later persuaded by us [ me and my wife and my chacha chachi ] was admitted to government hospital for treatment of psychiatry for almost 23 days in month of march and later she returned home and we provided her private nurse for 10 days and than in april she passed away . After her demise I was shocked and dismayed to know that my chacha chachi their sons and my grandfather conspired and got her to write a registered WILL during her stay with them . she has willed 50% of her share in my house and shop in favour of my chachi and 1 more house for which my mother was 1st allottee also to chachi’s name and lastly we have 1/3rd share in my grand-mother house which also has been willed to her. They have been threatening us about the some hand-written pages by mother accusing me and my wife of mistreating her and she having danger to her life from us , though NO FIR has ever been written nor did my mother ever made any attempt to disown me during her life time , her medical condition was such that she even accused and abused my kids [age 3 & 6] of malafide intentions During her entire life my mother has stayed with us , I have all her medical record history . all her medical bills , all her ID’s showing her to be staying with us . Also I am class I legal heir and with no brother and sister . lastly I have been paying all my property tax and IT tax return from the said property from time to time and I am in possession of all the said properties . I want to know :: 1. Can this WILL be challenged 2. Should I wait from them to get it probated 3. What all the points which are in my favour and against 4. Can they stop my rental income on the basis of registered WILL 5. Can I get criminal case registered against my chachi for having a registered WILL from a Psychiatry patient [though it was done almost 10 days prior to her hospitalization and they themselves brought her to get her admitted]