Enterprise vault for Distributed exchange environment

depends really on the number of users and the connection speed between the data centers.

Lots of solutions, but not knowing any of the details, it's hard to guess.
I suppose you could discuss this with a Symantec Systems Engineer, use the different sizing tools and what not to determine what kind of set up you should give them, I don't know what replaced SymIQ for Partners, but that should be your first stop

If i had to do it, without know anything about your environment i would have

Site A - With the most Users
EV10 SP4 on Windows Server 2012
 - All Vault Stores and Indexes on storage local to that data center
 - Vault Store Group hosted on the local SQL Server

SQL Server 2012 on Windows Server 2012 x64
 - Hosting the Directory, Monitoring, Auditing Databases
 - Hosting the Vault Store and Vault Store Group Databases for the EV Server located here

Site B - With the least users
EV10 SP4 on Windows Server 2012
 - All Vaul Stores and indexes on storage local to that data center
 - Vault Store Group hosted in Site B's SQL Server, not on the main directory SQL Server

SQL Server 2012 on Windows Server 2012
 - Hosting the Vault Store and Vault Store Group Databases for the EV Server located here

You *could* have both Data Centers use the same SQL Server, and you could have both Data Centers use the same Vault Store Group, but that would add a lot of traffic to the WAN between the two sites,  not just from SQL Calls back to the main data center, but from any shared parts that exist in the other sites vault store partitions.

On the flip side, you could also have it so each site mirrors each other, and if they do storage replication and SQL replication to each other, you can use the other DataCenter as disaster recovery.

I think to recommend a seperate installation between data centers since the WAN bandwidth is 1MB/S

do you a gree with me or we can Implement the suggested options with this bandwidth.

It depends on how large your environment is, how much data you already have going over the pipe etc, I would recommend checking this out, then thinking about how much data is likely to travel across the link with EV installed and see if you are going to come anywhere near saturation or not.

There are so many variables involved it is almost impossible to say one way or another from where we stand, trying to give advice on someone else's environment without knowing the full ins and outs is almost impossible unfortunately, without sounding funny you are more than likely the person in the best position to do that.