Yes, they will. As long as you are using the drums that are compatible with your system, said drums are compatible with all of the games in the Rock Band series.
Yes they are but instead of asking why dont you just try it out? =]
Of course! Did you know that guitar hero stuff can work on rock band and rock band instruments can work on guitar hero? Amazing huh?!
Yes.
Yes, all the instruments from the first game work on the 2nd.