Zero.
Lois Griffin is alive, but Stewie killed her in a simulation in the 100th episode
I think that would be either "Stewie Kills Lois" or "Lois Kills Stewie". Stewie gets upset that Lois didn't take him on vacation or something and he sets out and "kills" her.
No.
Lois
Technically no one killed him since the death was erased from the timeline by Stewie, however, since the "Who" wasn't the focus of the episode they never had anyone killing him, it was juts a randomly driven car.
the 100 episode was stewie kills Lois now the next one is Lois kills stewie
None of them technically. He was "killed" in Lois Kills Stewie but it turned out it was a computer simulation so he didn't actually die.
Family Guy - 1999 Lois Kills Stewie 6-5 is rated/received certificates of: Canada:13+ (Quebec)
Family Guy - 1999 Stewie Loves Lois 5-1 is rated/received certificates of: Canada:13+ (Quebec)
The two parter Stewie Kills Lois / Lois Kills Stewie originally aired in the Sixth Season.
Season 2, Episode 19 - "The Story On Page One"
This occurs in season 6 of Family Guy.