Its difficult my dear,

What you are talking is about sharing, If you want a decent private living 12500 is ok, but the saving at end of the month is not too good.
Yes if your wife is a professional too then you can count that full salary is saved.

The best possible idea to save is to make a property commitement back home, Take a loan in qatar and and keep paying. When your money/ property is appreciating back home, You are happy that you are settling your loan in riyal which is on a loser side as of now.

All the best.