1. You may need to install the Collector Agent at the DC1 with step in the link
Technical Tip : FSAE Standard mode installation procedure (Step by Step guide)
http://kb.fortinet.com/kb/microsites/search.do?cmd=displayKC&docType=kc&externalId=FD31882&sliceId=1&docTypeID=DT_KCARTICLE_1_1&dialogID=29647444&stateId=0%200%2029645986
1.1)Then you just need to follow the path in the DC1 to get " nstalldcagent" from DC1 to install in DC2 ,DC3 ,DC4. (So only DC1 will have the Collector Agent with GUI. But for the other DC ,it may not have.)
For 64 bits
C:\Program Files (x86)\Fortinet\FSAE\installdcagent
For 32 bits.
C:\Program Files\Fortinet\FSSO\installdcagent
(And it will has uninstalldcagent for you to use to uninstall only the DC agent also. )
and copy " installdcagent" from DC1 to install to DC 2 ,DC3 ,and DC4.
When you install ,it will ask the information of the Collector Agent that you may need to put in
Collector Agent IP address : (The AD server that has the Collector Agent (DC1) ,Collector agent with GUI and DC agent installed. )
Collector Agent listening port : (The default is 8002 )