The key here is "...list and manage".
You engaged these brokers to perform property management for you, correct? So, you had some form of property management agreement. I guess that's where "They were much more expensive than anyone else..." comes in, right? If that's true, then they represent you, the owner, and no one else in that aspect of your relationship. All their agency "duties" are to you.
But, you also say you hired them to "list" your property. Do you mean that the property is also for sale currently? If that's true, and there's a possibility that the tenant they secured for you wants to buy the property at some point, OR you're currently involved in a lease-purchase with the tenant, or the tenant has notified the brokers that they would like to buy the property, that's where a dual agency agreement would come in. Regarding the SALE of the property to this particular tenant.
Please tell us if you have a property management agreement OR only a listing agreement, or both.