Possession of House

We have an independent house at sagarpur in new delhi which is divided in two parts, front side belongs to my mother and backside is on my fathers name and having separate registered GPA. My sister suit a case in 2011 on my mothers property for ownership. she claims that property was purchased from her divorce alimoni amount.Earlier this property was on my uncle's name he has sold it to my mother but my sister is having agreement deed without any stamp n basis on that she tries to proof that it was given to her and says that my mother has made it on her name fradulently which is totally wrong and want my mothers portion on her name so filed a case which is going on since 5 years at dwarka court but didnt get stay order yet. Moreover she is staying at the back portion of the fathers property n also occupied front portion illegally which is on my mothers name at ground floor n also occupied one room in first floor where we are staying. I want to file a case to get my fathers portion vavcant but when i approached my lawyer for filing a suit for my fathers property to get vaccant he is suggesting me that not to do so because already one case is going on & said that my sister lawyers can co-relate with the mothers property n it will be very tough for us to proof n get the same vaccant. My parents wants to sell this property or else they want to make a gift deed on my name as soon as possible. I want to Now need best suggestion what can be done sooner with best possibilities so that it can be resolved as my sister are doing wrong activities day by day n we are getting rid of it now. My father is 66 years old with high BP. he want to sale his property as soon as possible but no local property dealer interested this disputed property. Please Advice