Can yo explain more, as I am not sure what you mean. Surely you only have one password which is your router password and all three items that need access use that password.
When you change ISP's you will,I assume, get a new router which you will stet up changing the default password of course. So if you change the default password to the one you are using with your existing router that will save any issues,I think.
You could, dependant on your new ISP, use your existing router, if it is one that you bought, obviously it will need to be set up for use with the new ISP but that is usually quite simple.