Cancellation of fixed marriage

We(their family too) fixed a marriage with their son of our daughter, in the month of April 2016 The groom met our daughter under the surveillance of both families , our daughter cleared her future plans and everything we also cleared and talked openly about our daughter plans and other aspects of marriage. We also asked them and they didn't say anything related to marriage requirements and other needful things. We waited for many months because they said that they'll complete the marriage by the end of 2016 we denied all the other groom families. And also booked all things including marriage gardens and other things. Now the groom party puts on a condition that if our daughter may get the job in their son's working city which is dubai, U.A.E , only then they will make their son marry our daughter and if she doesn't get the job so they will look onto someone else . This condition wasn't spoken by them before doing basic exchanges and fixing the marriage(roka) We have proofs of all the visits , roka, meets and other family activities and exchanges. Now they have cancelled the marriage by putting this useless condition and the boy and his family is mentally harassing us, our daughter's image is getting defamed. Because of breaking it at such moment. We have faced financial, mental, emotional and society damage. What legal action we can take?