They are first seen in "The Legend of the Gobblewonker" where their father. Manly Dan was teaching them how to fish without using a fishing rod but their fist as they cheer while watching their dad beat up a salmon. Later, as Dipper, Mabel, and Soos are running from Old Man McGucket who was using a giant robot, Manly Dan and his sons are knocked out of their boat then get hit by a rain of salmons and swim for their lives thinking the fish seek revenge.
In "Double Dipper", they appeared in a photograph that Wendy shows Dipper of her with them when they were kids.
The younger brother was seen riding the Farris wheel at the Mystery Shack Fair. Later the other two could be seen in the background using the strength tester.
They make a cameo near the end of "Fight Fighters", where they are seen with Manly Dan after coming back a camping trip with Wendy.
They reappear in "Summerween", trick-or-treating with their dad while they are dressed as Vikings and ram a giant log into someone's front door soon they could the candy.
- Accoding to Alex Hirsch; Wendy's three brothers' names are Marcus, Kevin and Gus.