Hi
Since both you and your brother in law are joint owner's of the property, your signature is mandatory for availing any loan on the property.
In absence of your signature, your property cannot be mortgaged (either by deposit of title deeds or by way of registered mortgage deed) and that any mortgage is totally invalid in eyes of law.
So you should file a cheating case against your brother in law and the financier.
Also you need to file a civil suit in the court to prevent any claims made by the financier on your ownership and possession of the property, given the fact that you were earlier the joint owner and now that you are claiming your ownership as 100% given the fact that you have purchased your brother in law's share of property as well.
Hope this information is useful.