You can sue the property manager for intentional interference with your right to quiet enjoyment of your property and business. You can also sue your fellow tenants with intentional or negligent interference with your business.

If you can establish your income (net and gross) prior to the problems with the property manager and the co-tenants and the current income as a result, in whole or in part, of their negligent and intentional actions, you can seek damages for the difference.

You know that they're going to claim the economy is the culprit for the slow down in your business, so you're going to need good, solid proof that your quiet enjoyment is being interfered with and that the change in your bottom line is the result of the property manager and your co-tenants.

You will need evidence or testimony of actual occurrences that support your position. For instance, the property manager comes in your store during business hours and haggles you in front of customers on a frequent basis, or the co-tenants tell their customers not to patronize your store or make it difficult for customers to access your store by removing/hiding signs, etc.

You certainly have a right to quiet enjoyment and to operate a business without interference.

My suggestion is to have an attorney write a letter demanding that each of them cease and desist their current activities, and if not, you will seek an injunction and subsequent damages against each of them, as businesses and individuals.