Shinkansen to Nikko query

Hello everyone! Been lurking here for the past couple of days and its really reassuring how helpful all the advice is.

Wanted to ask for some advice on what to do with the above.

Ive bought my group of 4 tickets from kitasenju to Shimo Imaichi on Klook and found the option for a private room for 1900 yen each (great, very cheap!).

Problem is its stating at the bottom to present it with a Nikko pass (which doesn't seem to be an option now that the train is tomorrow) or "purchase a basement fare ticket at the station" do a lot of shinkansen require these two tier tickets? And if so is it better to talk to someone at the station or just simply get a one way ticket from there to Shimo Imaichi?

Sorry for the long mindedness of the post. I just want to make sure I get everyone there properly!!!

by propergrim