Yes, Will Ferrell did sing in Step Brothers. In fact, Ferrell uses his own singing voice in most of his films. At the end of Step Brothers, Will Ferrell's character, Brennan, volunteers to oversee a prestigious event, the Catalina Wine Mixer.

Does Will Ferrell really sing opera?

Will Ferrell does his own singing. John C. Reilly does his own drumming.

Who sang in Fire saga?

Rachel McAdams sang the beginning of most of Fire Saga's songs, but the main vocal performance comes from Molly Sandén, AKA My Marianne. Eurovision fans will notice Sandén's name as she came third when she represented Sweden at the Junior Eurovision Song Contest in 2006.