Networking Question

network diagram here: http://dalgrim.com/files/network/Network%20Config.jpg
I'll start by saying I didn't create the network setup. Internet is connected to a firewall which has 2 wifi networks "Guest" and internal This is physically wired into the managed switch. The firewall is the DHCP server for all.

I purchased a NAS synology RS818rp+ and set it up with a dynamic link aggregation 4x1Gbit on the physical network

The problem is all internal wifi users can not see the NAS as they are on a different logical network.

What is the best way to fix this?

posssible:
1) add VPN rules?
2) Get the guy who setup the network to change the assignements of the internal wifi to a different IP and use a /23 on that and the wired placing them on the same logical network?
3) Change the IP assigned to internal wireless devices to the same network as physical wired.

note that this is not a 500 user location. This is a smaller remote office with <20 people. Even under a heavy guest load We'd never break 100 devices at once across all the networks.