There is a number of ways of doing.
1. You can setup a wireless router to a new internet connection. Witch would mean you would have two internet connection, and I don’t think you want to pay for that but it would be the easiest way.
2. You could setup a firewall between the router and your business computers. The firewall if setup correctly will block any traffic from the wireless network and the internet that you don’t want going to you business network.
ig. BUSINESS NETWORK —–> FIREWALL —-> WIRELESS ROUTER —-> INTERNET
3. Some wireless router have a VLAN option witch will let you VLAN your wireless network from your wired network but still let both use the WAN/Internet. This would make it so that your wireless network could not see your wired network.
There are other ways but the three I list above are probably the most common.