Construction and real estate company seeks real estate/brokerage software

We are a real estate developer based in northern Germany and are looking for real estate/brokerage software for a real estate project.

The following requirements must be met:

• Management of external agents
• Coordination of external agents’ collaboration: if Agent A has already entered a client into the client database and Agent B attempts to enter that exact same client again, a message should appear (“Client already exists”)
• Changes to this client’s data by Agent B should no longer be possible
• However, we as headquarters must have full access
• Access control, assignment of rights
• must ensure that clients are always served by only one external agent
• Management of properties listed within the project, including reservation and sale functions
• for PC (Windows-compatible) or as a smartphone app (compatible with Android, iOS)

This involves approximately 5 software workstations.