Provide two different networks with Internet while using a single ISP

Problem:
How to share a single Internet connection with 2 separate routers with both routers on a different network.  
I support a church that has a 25/25MB FIOS connection that they use for their office and business needs. Their network consists of a single SBS 2003 server with 16 workstations and 2 laptops. They have been running on a Linksys RV042 router for nearly 5 years with no problems and they has an exact backup RV042 that we’d like to use to provide wireless access for the different classes and groups that use the church at night during the week.
To completely cover the entire church we have 3 EnGenius Multifunction wirelesses AP’s that we ran CAT6 cable to from the RV042’s .
While we have been able to get the wireless network to work with one router the DHCP only running on the SBS2003, the problem has been that the laptops that connect wirelessly are receiving IP addresses from the server that are on the same network as the office systems and they would like for the public to receive IP addresses that are not on the same network as the office PCs.
When we use the two RV042 routers that provide two different networks (192.168.16.0/24 –office) and (192.168.1.0/24) for the wireless guests) It work fine until the DHCP service on the server would shutdown when it detected another DHCP service running and then the office PC’s started getting the wrong IPs. This also happened each time the server was rebooted the DHCP service would not start while DHCP was enabled on the second RV042.  
The RV042 labeled as “MAIN” is connected to a 24-port gigabit switch on port-1
The RV042 label as “WIFI” is connected to port-2 on the MAIN router and each of the 3 AP’s are directly connected to the WIFI router.  
I’ve tried using the different modes on the RV042 (Gateway and Router) and the DMZ port and every other cable configuration and yet can’t seem to get past this one.  
I was hoping to find a way to share the single Internet connection with two different routers without having to go to each church PC and enter a static IP and then disable DHCP on the server. It seems like this should be simple enough, though I have yet to find a solution.
How should we resolve providing two different networks with Internet while using a single ISP?  
Thank you!