I'd suggest chartering a taxi from MK. They should be able to provide a vehicle for six passengers plus luggage with an English-speaking driver - not a qualified tourist guide but capable of getting you to the places that you want to visit on your way to Yokohama and communicating in English:
https://www.tokyomk.com/fleet-en?lang=en

KM taxi can do the same - I have found them to be good, but not as good as MK. YMMV.
https://www.km-group.co.jp/en/taxi/index.html

if you really need a tourist guide to plan an itinerary for you and entertain you with tidbits of history and culture, that's another matter.