It isn't possible to sign a peace treaty with the Kadets. The idea of doing that would have been unthinkable to them.
You'd be better off doing that as the Mensheviks or SRs. Even then, you still need to make sure the Left SRs, or Internationalists for the Mensheviks, are in charge.
I have actually managed to get a peace treaty as the Kadets before, but it required spending the entire game boosting the left-Kadets via advisors and party cards so it isnt really worth it.
I dont quite remember since it was a few months ago, but I basically did nothing except the bare minimum to survive and increase left faction strengh through the advisors and ideology card whenever possible
