Killzone 1 is, Killzone 2 is not and Killzone 3 is.
View page
You can play the public beta for Killzone 3 on the 3rd of
February, 2011.
View page
Yes just like Killzone 2 was
View page
The Killzone series takes place in the distant future. To be
exact Killzone 3 takes place just minutes after the ending of
Killzone 2, which is November 2359 to May 2360.
View page
killzone 3 is exclusive to playstation so it won't be avilible
on any other console