Adnan wroteinstall custom firmware and try various little things like various forms of traffic shaping and network usage monitoring (could help split the bill), etc.
One word of advice, here. In many countries, the countries with most internet usage and consumption ("developed countries") the connection is usually fast enough, and the quota large enough (and the router pre-configured) so that nobody needs to worry about such aspects of optimising and watching connections.
Most such activities would happen at the ISP, on big bandwidth connections which would be shared, for example.
So the software that is available is usually geared towards that (network engineers, ISP grade hardware and software), that is why trying such advanced control of the connection on your consumer router hardware might be convoluted and not so much fun, in my experience.