Very interesting case... I thought these things happen only in movies or non-Indian cultures... In any case, if indeed your father has been sending you these messages, then these are indications that you are not making false allegations. There have been high-profiled cases where men have been booked based upon vulgar emails/SMS as evidence as they make a primafacie case that the men was upto something else too...
Now, regarding DCP, influence, etc. let me assure you that these do not matter any more if you are tactful. In fact, these people are themselves afraid of their own reputation in such cases. You can always approach his senior, Commissioner, for example.
If your father-in-law is a pervert, forget about Ramayana, Quran, Bible, etc. These books do not deal with such issues and there were no Courts and proper laws when these books were written.
Most important issue that you need to decide: YOU FILE ANY COMPLAINT ACCUSING YOUR FATHER-IN-LAW OF WHAT YOU ARE ALLEGING, THATS THE END OF YOUR MARRIAGE. If your statements are true and your husband is silent, you should get a divorce anyway, file appropriate police complaints and move on boldly because its disgusting for a father-in-law to do what you are alleging. If your allegations are false, you will be wrecking a family and then the Quran, Bible, Gita, etc. will come into play... Your husband can file for divorce based upon cruelty to him if your allegations are proved false. Karma finally catches up!