Seems to be a DNS issue.
When configuring a network adapter it needs:
IP: An IP address in the range of your network
netmask: in small networks 255.255.255.0 or /24
Gateway: in small networks the IP of your Router
DNS: in small networks same as Gateway, so IP of your Router
You can add the informations by editing the script in /etc/sysconfig/network-scripts/ as you already described or in the webinterface.
You only need to add the DNS IP to resolve your issue.
When using DHCP the client will get all information from the DHCP Server, in your case your Router.
When using it for your business please think about Backups and RAID. Backups are more important.