Thanks for all of your ideas. I really appreciate the time people put in to help refine my thinking.
We've camped on numerous occasions as a family and love it. We've also been to family camps where we don't control the schedule (the kids happily did scullery duties without being badgered, they also would stay to clean the mess hall, sweeping and so on, as well as getting involved in activities like abseiling, canoeing, ropes courses - both high and low ropes and so on). Linguistically and culturally we will be fine adjusting to difference as we speak Spanish at home. I also speak French and my eldest daughters are learning.
I've been really encouraged by the replies encouraging us to stay in the albergues. I would also agree that often the poorer behaviour isn't necessarily from the children. Our kids are tremendously respectful towards others (although not so generous towards each other!). I think the idea of preparation is really important and have taken those suggestions on board. In terms of communal living, I agree with the idea that we are already comfortable with the idea. (Beyond the sharing in our home, we are quite hospitable and have spent at least half of our kids lives hosting at least one other person with us for lots of different reasons)
I'm sympathetic to Joe's idea to start in Roncevallos, the first days with our littlun is perhaps a bigger concern of mine. I'm also torn though as I really want to walk in France too. Does anyone have a suggestion for a 3-5 day walk in France, to then have a break for a couple of days (maybe in SJPP) before heading on?
Regarding my son on the spectrum, lots of people don't notice initially, it is more evident in certain behaviours. I'm not concerned at all about his general behavior during the time, I'm just not particularly confident how he would respond to the difficulties I hear described like being riddled with bed bug bites and numerous blisters. The response to the physical demands I guess, that will only be evident once we are there. Also he has some peculiar behaviours, for example, his eldest sister told him (only once) that moths were flying spiders when he was very young, so he is now terrified of moths (we intervened but his fear stuck! Poor thing!)
How easy would it be to travel staying maybe 2-3 days in a row in albergues, then maybe 2 days in a hotel? Is availability difficult for large families? (4 adults, and 5 kids (16,14,12,8,3)).
Thank you for pointing out the idea to never carry our kids. It makes complete sense, but something I wasn't sure which way to lean.
Based on the suggestions, I think I really need to start testing the physical boundaries, such as the multiple day hikes now and how they respond.
I would be interested in how viable others think of prams/chariots are as I anticipate our baby will still need to sleep during the day for a couple of hours.