Technically there is no episode where Lois kills Stewie, Peter in fact kills Stewie.
The episodes you are referring to are the 2 part episodes, 'Stewie Kills Lois' & 'Lois Kills Stewie'
Season Three|Episode Twenty Road to Europe
"Patriot Games" & "Saving Private Brian"
Season 4 | Episode 20 | Patriot Games
Brian lost a $50 bet that Mike Tyson would win a celebrity boxing match with Carol Channing.
Season 4 episode 25
It was Stewie's nursery school teacher but it was Season Ten's Be Careful What You Fish For
Your question is vague to say the least but you might be describing Season 5|Episode 7 Chick Cancer when Brian tells Stewie "it's not your fault"
Because Brian bet Stewie Carol Channing would lose in a fight w/ Mike Tyson. She won so Brian owed Stewie $50.
Its the episode where Stewie and Brian are on a Trip to Aspen, Co to get Rupet back called Road to Rupert.
Season 5 episode 19
Season 3.
Brian tell Stewie the truth when they are stuck in the bank vault in the episode Brian & Stewie
Brian & Stewie's Emmy appearance & performance wasn't part of any Family Guy episode.
All of the "Road to" episodes are primarily Stewie and Brian centered episodes, also of the episode titled Brian and Stewie
Season 8|Episode 6 Quagmire's BabySeason 11|Episode 22Road To VegasIn Hand that Rocks the WheelchairSeason 09|Episode 12, an evil version of Stewie is cloned but not Brian.
Saving Private Brian
It was Stewie's nursery school teacher but it was Season Ten's Be Careful What You Fish For
Saving Private Brian.
yeah its in the episode 407 Brian the Bachelor watch it at familyguyx.net
"Brian Griffin's House of Payne"
Your question is vague to say the least but you might be describing Season 5|Episode 7 Chick Cancer when Brian tells Stewie "it's not your fault"
The evil Stewie clone does it in The Hand That Rocks the Cradle