Why did Hashem confer the title of "ha'Resha'im ha'Eileh" upon Dasan and Aviram more that on the two hundred and fifty men?
Targum Yonasan: Hashem was referring to the numerous times that they sinned since their youth. 1
Why would anyone who was found in the vicinity of Korach, Dasan and Aviram or who touched anything belonging to them perish?
Ramban #1: The Pasuk needs to be inverted - with "Pen Tisafu ... " following "Suru Na me'Al ha'Anashim ha'Eleh", 1 and "ve'Al Tig'u ... ", as an independent warning not to attempt to take any of their possessions, which were Cherem (prohibited to benefit from).
Ramban #2 (citing Ibn Ezra): Anybody lingering behind in order to salvage any of their belongings would suffer the same fate as them. 2
Seforno: Because they were not worthy of being saved from the current plague.