Section 376/494/323 IPC

My brother-in-law is accused under the section 376/494/323 IPC by a lady who was staying with them with her teenage boy to take care of my sister i.e his wife who is sick. It has been nearly a month that lady and her son has been staying. That lady came when my sister was hospitalised to take care of her as my niece was appearing for exams and it was that lady who asked my brother in law to let her keep care of my sis. Saturday she suddenly created a scene and told everyone my brother in law is having affair with her and that she is married to her and all that. So my brother in law called the police and they both were taken to p.s. The police there didn't let my brother in law lodge an FIR but let the lady do it first saying the man cannot lodge FIR now although it was my brother in law who informed the police. Now he is arrested under these sections as they accused is arrested first and then prove innocence. But the main thing is that the rape is a False allegation and even marriage. And my brother-in-law was never alone with that lady when my sis was hospitalised. That lady alleged him that he raped her when my sis was hospitalised but he always stayed with my sis at hospital with my niece every night till my sis was discharged. And she was in hospital about almost a month ago and now that lady has filed FIR. And that lady was left by her husband few years back too. Can you suggest anything I can do to get my brother in law out of jail as soon as possible. How can his family help? As he was with his family all the time and never alone even once with that lady. What to do to prove my brother in law's innocence?