It depends: are they hooked up to the same router?If not, don't.If so, go ahead.
It doesn't matter. You can put your key in wherever. I know cause I went to my friends house, put my key and it worked and we have different routers!
I want to play blockland on my laptop. Could i use the key?
Sharing keys with a freind is a no-no.Badspot is probably de-activating your key as we speak. :)