do i need to play vermintide 1 first?

Playing V1 is not at all necessary to enjoy V2. You might miss part of the story of Vermintide 1, but V2's prologue and the dialogue between the characters fill the gap, so you won't be lost.

In both cases the story is not the big focus of the game, however, the gameplay is. The story helps build the world and the reason for each mission, rather than being a narrative focus.