If you have a "normal" BT ADSL line then any ADSL router will do (you only have to worry if you have a Virgin CABLE connection as cable routers are different from ADSL routers).
Wireless routers also allow connection by cable so if one your PCs is near the router you can use a standard RJ45 Ethernet cable for that.
I only have one laptop connected wirelessly to my router so not sure what effect having 3 connected wirelessly would have (although if you can connect one via a wire that only leave 2 to connect wirelesly).