I had originally wanted to go to Jimbocho Den, but they are fully booked up during our dates. Looking around, I stumbled upon Kanda and thought it might be a good alternative. Has anyone been there and can recommend it (or advise against)?

The only complicating factor is that we will be taking my FIL and his girlfriend, so if there are "weird" things on the menu, they may not be game. The last thing I want to is to insult the chef because my FIL won't try monkfish liver or somesuch. They claim to tailor the menu to the diners, but worth asking the question.

Oh, Kanda the restaurant not Kanda the Tokyo district.

Kanda-san does seem to have the right attitude: www.nihonryori-kanda.com/english/menu/

Kavey?

Yep, Kanda the restaurant. It is proving hard to find much in the way of reviews.

You could ask / search on Chowhound Japan board?

Kanda gets 3.91 stars on tabelog. That's high, but not the highest. Looks like it's ranked 5th in its neighbourhood - which seems to be the very wide area of Roppongi, Nogizaka and Nishi-Azabu. Tabelog is the site the Japanese swear by. If you don't read Japanese, the google-translations of the actual reviews are usually impenetrable so we tend to go by stars/ranking alone.
https://tabelog.com/en/tokyo/A1307/A130701/13005439/

Did you go?

No, we did not go to Kanda. By the time we went to book, their last table was gone. We ended up at Sublime instead, which was phenomenal.

Have you recovered from the embarrassment that FIL caused at Sublime or did you leave him at home?

FIL was well-behaved at Sublime. It helps that the food there is influenced by New Nordic cooking (the chef staged at Marchal and AOC in Copenhagen), so a little more familiar to him. For the most part, he was a good sport during the trip, save a stay at a ryokan where he left a day early as he hated sleeping on a futon. We did leave him to his own devices for a couple of other meals and he ate Western food in the hotel both times.

He used to be much more adventurous than he is now. I'm not sure if it is just age-related stubbornness or what. I mean, he used to eat sushi without a problem, but we get to Japan and he didn't seem to want to touch even a tuna roll.