The below should do what you're after. Save it as a vbs file, and call from the command line via cscript, e.g.
cscript localadmins.vbs
It will connect to each server listed in the file C:\serverlist.txt, and tell you who's in the Administrators group. The txt file should just have each server name in a single list, no other text or it will fail.
It's pretty basic but you get the general gist...