I am wondering how to use my brothers IP address instead of my own. I want to be able to access a specific website and geographical location is important.
I'm in the south and my brother is in the north. At the moment I'm using teamviewer to access his pc and surf from there but this is inconvenient for him
Depending on his ISP and the physical setup he has, you may be able to setup a proxy server at his location. That would allow you to connect to the proxy server from your location funneling your Internat activities through his IP. Be aware that his ISP may have a problem with him running a proxy server and it will be a noticeably slower connection then not using a proxy.
A better solution my be using TOR. It is a Firefox browser setup specifically to use proxies. You can usually select the region you want your IP to be from. It is also slow and is blocked by some websites.
I've used TeamViewer for remotely troubleshooting problems on PCs, but as that interrupts the use of the system by that person, as you note, if I know I may need to periodically test access to a web server or other server so that it appears my connection is originating from the IP address of someone who has a system running Microsoft Windows, I've used the free AnalogX Proxy program. You will need to create any needed firewall rules on the PC, if it is running host-based firewall software, such as the firewall software provided by Microsoft or third-party vendors, and will also need to configure any router/firewall which provides access for the PC to the Internet so that it also has an appropriate firewall rule or port forwarding configuration to allow connectivity through on the port you have chosen for the proxy software and forward that connectivity to the PC.
Note: You need to ensure you aren't making the proxy service available to anyone on the Internet who may be searching for open proxies, perhaps to use for nefarious purposes. So you need to restrict access to the proxy server to just your own IP address through appropriate firewall rules. Don't count on no one else ever discovering that the system is functioning as a web proxy as there are people who scour the Internet for such systems.
I more frequently install Secure Shell (SSH) server software. There are a number of free alternatives; even some of the commercial products can be used for free if they are used for personal use. E.g, some I've used include Copss, Bitvise SSH Server, freeSSHd, and PowerShell SSH Server. You can then use an SSH client program on your PC, such as PuTTY, which is free to connect to the other system. The SSH connection will give you a command line interface on the other system, but you can also configure the SSH client, such as PuTTY, to create a Socket Secure (SOCKS) proxy server for the remote system, e.g., see public key cryptography, if you prefer, so that the SSH server only allows connectivity to your system, which presents a private key that matches a public key stored at the server end.
For either the HTTP proxy provided by the AnalogX proxy software or the SOCKS proxy approach, you will need to configure your browser to use the proxy server. Most commonly used browsers support proxying. Note: if you use the SOCKS proxy approach, you need to configure the browser specifically to use SOCKS as the proxying method.
With either proxying method, websites should then see your brother's IP address as the address from which connectivity has originated.