Children rights

Sir/madam I am a student (17yrs) i have my sister (21yrs) she is graduate. My mother and us are living separate as my father (59yrs)(he is working as BM in SBI) is living with another woman (age will be approx 30-33) i don't know exactly. I need to know that he is going to retire soon and he will get a good amount of retirement money and he doesn't provide any maintenance ( If i call sometime he provide 2 3 thousand only. My mother when she found out that he is having affair she filled a maintenance case but it didn't got ordered ( and the case was out of station as my mother filled case where my father was working city) witch was 1night journey from our hometown. So everytime when the hearing was there my mother went but nothing got in results. Then she held out hopes that she spend so much money but didn't got any result and i think and my mother too ( our lawyer who was local of that city) was making the case lengthy and he never report us right information.. Also after 4 5 yrs case we didn't do anything and father also as he told us that he will give us some amount infront of his senior in his branch ..then he gave 10thousand 2 or 3 months then stopped also he doesn't provide the money from his account he only does cash deposit till now he nver used his account to transfer money in us . After yrs when we heard some rumour that he is been telling his relatives that he has got devorced but my mother didn't sign till now . And when we call our lawyer his phone was switched off from ages.. So we consult a local lawyer from our hometown she told us that "i think he has withdrawn his case please check online from app from case number and it was true" then we told her that our lawyer didn't informed+ not got any letter... So she told file a case now so his last moment service will stop + all his money will be also stop..also told us to file a case from children too for his pension seperation...PF and etc Please help me mother don't have hope now as she is supporting us alone and she tells that our studies is effecting this all but i feel we should fight but.. We don't have money too we are suffering and lawyers ask money first for anything and court delays too much... I don't know what to do please help me..