Is it necessary to watch dead or alive 1 first?

Well, I haven't watched the sequels yet as I'm writing this but the second and third DOAs are unrelated to the first one's story. Same actors, different characters. And If you do watch the ending of DOA 1, you will see that no one COULD follow that story in a way that makes any sense.. I won't spoil it, it's insane.

Not really. Both movies are connected only because of the title.
The film have some of the actors of the first one, but they played different characters.

Prostitute: What the *beep* are you doing?
Johnny: I'm gonna kill a bunch of people.