LAN split and shared resource

I am trying to reconfigure a pre-existing network that at one point was one large network using the same ISP but now has been split with one company using a certain ISP and the other using a different ISP.

CO1 AND CO2 have their own ISP and router/gateway. Then from there they feed into the appropriate switches for their LAN.
At this point they are both independent and have no contact with each other.

Then, add in a application database. It has 2 NICs, one configured (statically) with CO1 gateway/IP scheme and connected to it's switches, the other configured (statically) with CO2 gateway/IP scheme and connected to it's switches.

That is the only common point of connection. None of the switches on one LAN connect to the switches on the other LAN.

The application database box is not on either workgroup, it is a different workgroup name. Both of the other workgroups see this box. The application database box is called APPBOX (for example) and is on the APP workgroup. The other two LANs are CO1 and CO2. I can go to either one of those networks, type in \\appbox and see the appropriate directories.

The problem is that on occasion CO2 network requires me to reboot, then ping the NIC and browse to appropriate directory to be able to launch the application (it searches for the proper data path).

I am wondering if a VLAN setup would help solve some of this? I have a managed switch that supports VLAN.

Any thoughts?

See attached image for my rough diagram of this layout...The 1 and 2's are which company the workstation belongs to...