real estate small business fraud?

Couple months ago, my family purchased a small yogurt shop in California. It was the first business purchase in the U.S. and we bought this business through a realtor who her husband is the previous owner of this yogurt shop.
During the process of it, we asked the previous owner and the realtor if there will be other yogurt shop coming, and their answer was 'no.'
We purchased the business, trusting them 100%. We increased the sale for the next three months. That is, until a bigger/cheaper yogurt shop opens few blocks away from our store. Our sales dramatically decreased exactly from the day that store opened.
We contacted the previous owner and the realtor (because they are husband and a wife) to demand for an explanation.
They kept saying 'honest God' that they did not know, and actually accused us of killing the business (remind you that we increased the sales for three months).
We tried to resolve this matter in amicable way possible, but the realtor and previous owner refused to cooperate in any matter.

So, we did our own investigation.
We found:
- the bigger yogurt store started construction on two months before our purchase of the business.
- the manager of the yogurt shop (who also worked for the previous owner) told that other yogurt shop was coming.
- the bigger yogurt shop was using billboard to advertise its coming and we have material evidences and witness that the previous owner did know that the other yogurt shop was coming.
- recently found out that this couple had fraud history in another state (NV).

Their reaction:
- they have indirectly accused me by publishing an article of the bad management kills the business.
- they are false advertising that our store earns a lot to sell other yogurt franchise (the previous owner has the license to sell franchise in the location we live).
- they are telling other people that this does not affect because the flavor of our yogurt is different from the bigger/cheaper yogurt store.
- they are going to the court if we are going to the court.

We have sent a letter for an investigation to DRE to suspend realtor's license.

We are also seeking an attorney help to unwind the deal and filing for a fraud, but we also want to receive some of your professional comments and suggestions of what we should do.

Our biggest concern is that they have previous fraud history and they may run away again. Attorney fee is also very high. We believe that they may know all these and may use it for their advantage that not many people really pursue the case to the court. Also, if they hide their assets, we heard it's difficult to recover the fees.