Facebook/Twitter login only vs. Facebook/Twitter signup and login separately

I have searched for this topic here, but haven't found solid answers for the problem.

So the situation is this: we are creating the authentication screens for a mobile app and we are not sure which social login/signup flow should we choose.

1. We have 4 buttons: Login with Facebook, Login with Twitter, Login, Signup. In this case, if you want first time login with Facebook you also get to signup. The other two actions for the users with email.

   Pros:

   • one button for social connect
   • the elements takes less space
   • they fit into one screen.
   • "simpler" flow.

   Cons:

   • accepting legal things /e.g. privacy policy/ for first time through this flow might be a little difficult to implement
   • might be confusing for first timers that they instantly "log in" with fb.

2. We have 6 buttons: Signup with Facebook, Login with Facebook, Signup with Twitter, Login with Twitter, Signup, Login. In this case, if you want first time login with Facebook you also get to signup. The other two actions for the users with email.

   Pros:

   • no confusion for the user about the behavior

   Cons:

   • the elements take more place
   • we definitely have to make 2 seperate screens for login and signup, so the authentication flow will be longer

Could you please share your thoughts/best practices? Thanks!