The fourth season of the Sibling Rivalries series has ran from August 15 to November 17, 2015.
Originally the season contained the comics "A Family Pet" to "Feeling Peachy", which was a total of 16 comics, before GTA Nerd decided to split the season in half and give all comics from "A Family Pet" to "Like Father, Like Sons (And Daughter)" to Season 3, which was originally made up of four comics ("Best Brother" to "Meet The Robots!").
This series introduces many new characters, including the Wilson family, as well as Aiden Wilson, the McReary siblings' new half-sibling. However the character has since been removed from the franchise.
- Patrick McReary (8/8)
- Francis McReary (8/8)
- Gerald McReary (8/8)
- Derrick McReary (8/8)
- Kate McReary (8/8)
- Maureen McReary (8/8)
- Hector Wilson (8/8)
- Aiden Wilson (5/8)
- Angel Chacon (4/8)
- Salvador Real (6/8)
- Joel Gonzales (1/8)
- Louis Wilson
- Carol Wilson
- Troy Wilson
- Adrian Wilson
- Samantha Wilson
- Armando Vasquez
- Braulio Guillen
- Mr. Guillen
- Mrs. Guillen
- Aiden Wilson
- The Step-Cousins Wilson (Release date: August 12, 2015)
- The Return of Armando Vasquez (Release date: August 25, 2015)
- Portrait of a Football Player (Release date: September 2, 2015)
- Wouldn't It Be Nice? (Release date: September 8, 2015)
- The Amnesia Act of 2015 (Release date: September 19, 2015)
- One Tough Break-Up (Release date: October 20, 2015)
- Haunted House of Horror (Release date: November 2, 2015)
- Feeling Peachy (Release date: November 17, 2015)
- Season 4's cover is the first one to actually show the McReary-Wilson family's living room (Seasons 1-3's covers feature an unspecified location on their covers).
- For this season, the logo of the series was slightly changed. This updated logo was also used for Season 5's artwork.
- Angel Chacon was absent in "The Step-Cousins Wilson", "The Return of Armando Vasquez", "The Amnesia Act of 2015", and "Feeling Peachy", which is a total of four times in the season. Salvador Real did not appear in "The Step-Cousins Wilson" or "The Amnesia Act of 2015", which was only twice in the season. This means Salvador appears in more comics in the season than Angel.
- This is the second season to remain only in one year (2015), the first being Season 1.