how i force users/clients to target one file server out of 3 servers in 3 different sites.

Hi Experts,

I have 3 sites and all 3 sites have File servers which are in sync with DFSR for similar data available across 3 sites. i created 3 namespaces for Data, Roaming Profiles for terminal services users and User Personal Drive. All these 3 folder locations are in FULL sync with DFSR

I am having issues in following:

1. how can i force all users from all 3 sites to use main File Server in main site.
2. how can i force users to connect to their local site file server in case of main site failure.
3. how can i force users to failback to main site file server after recovery of main site.
4. is file locking is possible with DFS-R.

any help in right direction is appreciated.

Thanks

Ajay