1. Your mother got 8 L during divorse settlement with the complete custody / responsability of child . She would have secured a part of it as a fixed deposit to secure your future. When divorce decree is passed , often the amount is decided considering sustainability of wife alongwith security for future of the child which your father has already paid. Ofcouse the part for child's security is not saved by your mother as desired which is causing financial difficulties to you now..
2. Secondly , You have a past of complicated relations in your family . Filing another suite on your father will create further bitterness/ emotional stress and may not bring any good to you .
3. Ethically its not justified to rip off your father again if he is not willing to support you . You are educated , capable and not handicapped . You can sustain your self by finding a job if you want . As a matter of fact in many developed nations like USA , Australia , Canada many high school students work part time and gain financial independence and experience . This helps them to develop the right attitude towards work and be successful in the longer run . While in india people keep on studying till mid 20's to 30's age and often find it difficult to adjust in work enviournment due to lack of practical experience and wrong attitude .
4. Take this as an opportunity to prove yourself and save the money which you are thinking to waste on hiring lawyers.
5. Try to maintain good and healthy relationship with your mother as well as father ( Give love to expect as willing support) . Your past was certainly out of your control but try to control your life in a healthy and positive manner . Try to get a loan from any of well wishers ( if you can ) which you can return once you be a CA. Remember its not always your qualification but your attitude towards life which can make you sucessful . Dont be afraid of challanges and create a passive envoiurnment aroung you so that you can grow further.