If your father in law is compromising on all the aspects with you then you can turn hostile during witness examination when you will examined in chief.
It cannot be predicted that if your father in law may take any other vindictive action in furtherance, however you are at your liberty to lodge a fresh complaint then.
The public prosecutor will do his duty because he is a government servant.
No lawyer can argue your case even if you engage one, the lawyer you may engage cannot travel beyond assisting prosecution, hence there is no use of it.
An unregistered compromise deed is not enforceable in law, it can be obtained for the sake of threatening him.
1. You can turn hostile witness only when you enter into a compromise with him, therefore it is not losing your case, but it is as good as he remains silent after that especially when a compromise has been arrived at mentioning all the incidents.
2. You are the complainant hence you cannot file a quash petition.
If her files a quash petition then you may have to support his quash petition by filing no objection to it stating that a compromise has been arrived between you both, which will be recorded in the order.