Hi Pete. Let’s start with your last question – you’re almost certainly not going to be able to get your old car back. Even if you manage to get a refund, you are likely to get the part-exchange value for your car rather than the car itself.
The whole operation sounds very dodgy, and it’s quite possible that the brothers are working this way to try and avoid their legal responsibilities as a dealership.
I would suggest getting some legal advice, as a consumer lawyer will be able to look at the original advertisement, the vehicle contract or sales order, the invoice and any other paperwork to help establish your rights.