Is Probate required for a Registered Will

I am sole beneficiary to my aunts RegisteredWill,duly registered in Delhi. She passed away 18 months ago.She made her Will at the age of 83 during the onset of her terminal illness 16 months before she passed away.She was never married& has no class1 heirs.I &my mother(sister) were the closest to her, though she has 2 more brothers who she never liked and never spoke to for several years.She has clearly stated her dislike for them in her Will. The 2 brothers have challenged her Will & my substitution in a property in Uttar Pradesh but have not challenged her Registered Will here.She was a resident of NewDelhi and had her main property here in Delhi and has 1 in UP. The estate values are high & I have for the last 15 months fighting my case in UP district court. My lawyer advises me to go for a probate since he says I get 3 years from the time my Will is challenged anywhere??? Is probate required for a Registered Delhi Will? When do I have to give the Probate fee & what %age?