as someone above said, if your father reverted to the local religion, then he is entitled to the marriage.

But you can track his marriage through our embassy 'cause he need a certification from our embassy for such marriage to take place.

As to your rights, it remains intact but I suggest that you forego about the property (if there is really) here in Qatar.

The only way you can have get your fair share is if he passes away and his remains brought back in our country, then your mother being the legally original wife, can claim all that he left (insurance, benefits, properties if you have one there, etc etc.).