The problem here is that your devices are all using the ISP router as the gateway to the internet, which means that they aren't going to be tunneled through the VPN. You need to tell your client devices to use the OpenWrt device as the gateway in order to have the traffic go through the tunnel.
You can see if your setup generally works by setting a client device with manual/static IP information... you need to populate the IP, subnet mask, dns, and router/gateway. To do this properly, you will want to set the IP to an address within your network, but outside the DHCP pool to avoid conflicts. Subnet mask will be the same as you see currently. Gateway/router will be the IP of the OpenWrt device, and the DNS could be the same OpenWrt address, a public DNS like 8.8.8.8, or a DNS server from the VPN service.
Give that a shot as a test. If it works, you know the OpenWrt side of things is working, and you just have to make some other modifications to how your network operates with respect to the DHCP server.