Can I sue or call the police first?

First of all, don't vouch for others casually. This will not only harm yourself, but also harm your family.

Secondly, if Couple A carries out this behavior many times, it should constitute a crime of fraud. You can file a lawsuit with the public security organ. But there also has to be some evidence. For example, you can sue together with previous victims. Generally speaking, the court will not directly accept criminal cases in this area, but you can file a lawsuit with the court from a civil perspective.

Again, it is best to hire a professional lawyer to resolve this lawsuit. After all, it involves the transfer of property, and moving evidence is easy with the help of a lawyer.