Can an advocate charge interest in addition to the fee percentage

My brother met with a motor accident in bangalore in mid 2013 & had several serious & permanent injuries. The expenses of his treatment had gone upto 15Lakhs and is still continuing. The lawyer took advantage of my parents inablilty to understand the language as well as the procedures of the court. She filed arguement stating only fractures, while my brother was admitted in ICU in a serious condition with multiple head, chest & abdomen injuries, his liver was cut due to impact of the accident, his lower foot 'tenon' is permanently damaged because of which he has foot drop & has to use foot support to walk. None of the were mentioned in the argument filed. The judgment was completed in Jan 2017 & the amount was only two third of the treatment amount. More over the Lawyer who had our case harassed him and took a charge of 12% of the judgment amount along with 8% interest mentioned by the court. Is it legal for the lawyer to charge the client on the interest amount also?. what is supposed to be the amount to be paid to the lawyer, Is it the balance amount after reducing the expenses bills which we presented as proof??