This is Vitamin String Quartet, an LA-based group that began doing classical covers of rock songs in 1999 and has since branched out to include pop.
3.
"Thrift Shop" by Macklemore and Ryan Lewis
14.
"Somebody That I Used To Know" by Gotye
19.
"Shake It Out" by Florence + the Machine
20.
"Home" by Edward Sharpe and the Magnetic Zeros