Villa and Dortmund are underdogs so going through to the SF is going to be hard but not impossible. Porto were underdogs in 2004 but won the CL because Jose Mourinho had a talented team. They won the Primeira Liga, Taça de Portugal and UEFA Cup in 2003.
Aston Villa and Dortmund are two underdogs in quarter final phase of Champions League but recall some underdogs like Monaco, Porto, and even Dortmund in some seasons, they managed to go to final matches as underdogs for several times. They are weaker than themselves some seasons ago but chance for making another surprising season in Champions League is not impossible for Dortmund.