whenever I activate NTT assemble and install NTT it does not start from steam. If I try to run the NuclearThroneTogether.exe it will load but I can not use frog or skeleton. How can I fix this

This is not the most specific. If by "cannot use" you mean that they are locked, that is because they have default unlock conditions - Frog is unlocked for getting a golden frog pistol, and Skeleton is unlocked for becoming Skeleton. In multiplayer, everything is unlocked by default.