I had this question/problem a few months ago and after many hours of painful research, I found a solution. First of all, to my knowledge you cannot use 2 or more routers on the same Wan or internet connection. What you need is 1 main router and the others will need to be 1 or more wireless access points. I learned very quickly that most good wireless AP's are somewhat pricey. There is 1 excellent solution to this problem and that is to convert a wireless router into a wireless access point. My personal choice for equipment is Linksys, I will not claim that Linksys is the best but this equipment has worked well for me in the past few years. The firmware in most routers is Linux based which therefore makes it open source, to an extent. This holds true for most brands of routers, not just Linksys. A few experts have created a firmware program to change many routers into access points. You can go here
DD-WRT for the details and supported software list, and a link to download the correct firmware. Be sure to read ALL instructions first because otherwise you can end up bricking your router. The nice thing about this firmware is that you can buy one of the WRT54g or gs routers that are in every store or internet store for about $50 US and convert it into a $600 wireless access point. This access point can then be connected wirelessly to your router plus you also have 4 ethernet ports that can be used for any equipment that you need to connect to the internet or your Lan if needed. The DD-WRT software is available for most other routers, there is a huge listing of other suported routers at the above link. They will list the version needed and links to very detailed instructions on how to set it up.
This is not hackware and it is legal since almost all router firmware is written in Linux so I believe it is all open source. The people that have created this are based in Germany at the DD-WRT website.
I am not an expert by any means on networking but the experts here can provide details on network settings etc. far better than I can.
I am currently setting up a new network using the WRT600N 2 channel router with a few wireless access points and 2 of the new brother laser printers that each have built in wireless print servers. So far it has worked well except for a few connection problems which will hopefully be worked out soon. I can see the router from over 1 mile away so I believe it has some distance.