Thanks for the replies. Talking with the family is excellent advice, thanks!
I have twins and a bit older brother so at the time all 3 will be 15 years old. A much different age than our last trips, and not nearly as easy to motivate. The biggest motivator for them now is friends. We are lucky to have one friend who recently moved to Cambridge, so that is a definite stop on our list. We also have a friend with an older kid who is a camp councilor, and has tons of fun with our kids. They live in Todmorden. Their son may join us on the adventure, which will make every location we go to much more attractive for the kids. Another family who often travels to Germany may join us for some part of the trip. We have friends with a kid the same age that lives in Paris. Our kids have not met, but they will likely enjoy the company. I also have a cousin in Rome. She's older than me, but loves kids and she will make the experience fun for them I'm sure. She may also join us at the eclipse.
I'd say that at least 90% of the motivation for the kids is friends, so if the visits work out, then the whole trip will turn out better.
Other than the friends, interests include sailing for all three and myself, but mostly for one of the twins. The friend in Cambridge was part of the same jr sailing program here in Santa Cruz, so we may have some sailing near Cambridge. The other twin has some interest in architecture. Not formally, but he does enjoy making interesting buildings, and places in minecraft. He recently tried to make an english pub. I'm sure that there will be more interesting architecture than you can shake a stick at all over Europe, and Tunisia, but I don't have a list of places. The third kid really likes to build motorized things. Trains used to be his thing, and I hope that he would get back into them in Europe. I do want to focus on trains for travel, and would love to do a sleeper train in Italy, and the train/ferry to Sicily on our way to Tunisia.
I put my priorities below the kids, otherwise I'll dominate the trip with things that are boring to them. I do have interest in history in general, but also astronomy, and science. I would like to visit places where my ancestors came from. One side of my family emigrated to the US from Bitonto Italy, and some town outside of Naples sometime around 1900. I have french Canadian heritage, but it was at something like 400 years ago that they traveled to Canada. My wife is African, but does not know from where.
A lot I know. My desire is for the trip to be 2 months, but I don't quite have buy-in for that, so we'll see if I can motivate them. I generally make a google "my maps" map to lay out possible places to visit, and dial in the trip. That has worked really well in the past. I start by filling it with way more places than we have time to visit. I filter it down over time to the spots that will make a good path with enough time at each location. So any ideas you have that fit can go into the early draft of the may. They may or may-not make it to the final revision.
Thanks for your feedback! -- one thing I do need to figure out early is travel. I really like the idea of getting a euro rail pass, but need to figure out which one to get, when the pass for that time will be available, and if the pass can be upgraded if we change our minds.