Got this info online....
Here's the complete list of songs in the movie Step Brothers in the order they appeared in the movie. They did not release a soundtrack album, but the videos and downloads for the songs are at the link below:
A-Punk - Vampire Weekend
North American Scum - LCD Soundsystem
Hairy Balls - John C. Reilly
Captain Benevant & His Ragtag Crew - Adam McKay and Steve Weisberg
Ice Ice Baby - Vanilla Ice
Breathe and Stop - Q-Tip
Sweet Child O' Mine - W. Axl Rose, Saul Hudson, Michael McKagan, Jeffrey Isbell and Steven Adler
Brother - Lee Ferrell and Hal Radcliff
Learn - Dizzee Rascal
You Make My Dreams - Hall & Oates
This is How We Do It - Montell Jordan, Oji Pierce and Ricky Walters
Live on Stage - Dilated Peoples
Tristan and Isolde - Richard Wagner
Something to Talk About - Will Ferrell
You're on My Mind - KO & the Knockouts
Under Pressure - Oz Ravbon and Amir Efrat
Boats 'N Hoes - Will Ferrell and John C. Reilly
A Marshmallow World - Brenda Lee
Family Bible - Rick Logan
Back and Forth - Jon Brion
Slow Burn - Set the Control
Keeping the Faith - Billy Joel
The Longest Time - Billy Joel
Por Ti Volare - Will Ferrell
Father Christmas - Kinks
The Impression That I Get - Mighty Mighty Bosstones
Derby Day - Cheeseburger
http://www.reelsoundtrack.com/index.php?act=movie_details&id=47401
Also, the person said Jon Brion did the original music for the movie, so the song might be one of his instead of one of the ones listed.
I know essentially half the listed songs and I know none of them are the one in the vid.