I wore mostly longer shorts and capris. I don't remember wearing jeans until we transferred to Paris after the
ABD. I think I remember our guides mentioning that we were getting warmer weather than usual. I think it was in the high 70s low 80s mostly. We were lucky to avoid most rain. I did have a foldable travel windbreaker that I kept in my purse to pull out as needed. Our Neuschwanstein day was cooler than the others.
There is a great photo op on the bridge across from Neuschwanstein. You could coordinate the family that day (from the waist up, at least) if you're looking for that next Christmas card photo (if you're into that thing). You are doing a lot of walking up and down that day, so nothing crazy, but some in our group had cute scarfs, and I was happy I had at least taken time for makeup and hair even though it was an early morning. I'm talking more of a cute casual look if you want to plan for a specific family pic. The guides will take a LOT of individual family and whole group photos along the way.
Shoes - A lot of cobblestones, so shoes with heels are not the easiest. Walking or athletic shoes/sandals are fine for most of the touring/exploring. Ballet flats or a shoe with more of a block heel would work better if you're taking anything nicer for evening. It really isn't necessary and is really a matter of preference. It wasn't like a cruise where you dressed for dinner each day. I dressed up a little more for dinner at the castle and for our last night, but I wore patent ballet flats or wedge sandals for dinners. Nothing fancy.