Lost passphrase

Use one of the devices already connected and enter routerlogin.com into a browser.  This will connect you to the router's setup screens.  The default username and password to log in are admin and password.  Once logged in, go to the Wireless settings.  There, you will see the Wi-Fi passwords. 

If you can't log into the router, then you may have to reset it to factory settings.  Put and hold the physical reset button for about 8 to 10 seconds until all of the lights flash.  Then release the button and wait a few minutes for the router to reboot.  You will need to set up the router as if it new out of the box.