My 2 cents based on my Europe trip (Greece and one 10-hour nighttime layover in London) and other travels abroad:
I think the 6D + 24-105mm would serve you really well. I would even be okay for the entire trip with just that body and that lens. If weight is no concern, I would throw in the 17-40mm and maybe the 50 1.8. Some people advise bringing a second body in case something happens (so you don't end up stuck without a DSLR), but I've never really done that. I did bring both my old 6D and 7D2 to Japan once, but I regretted it and ended up using just the 6D the entire time.
I went on my Europe trip with a 6D II, 24-70mm f/4L, Sigma 35mm 1.4 Art, and 50mm 1.8. I shot with the 24-70mm 99.9% of the time. That's not an exaggeration: I used the 35mm 1.4 maybe once, and I believe not even once for the 50mm 1.8.
The reason I ended up using the 24-70 the entire time boils down to: 1) as much as I love my prime lenses, changing lens on a cobblestone street w/ a ton of people/tourists around you (and potentially bumping into you) is a HUGE turn-off; 2) the ~4-stop image stabilization on the 24-70 (or the 24-105) is extremely handy--the attached shot, taken handheld at 1/6 of a second, would not have been possible without the image stabilization; 3) if you're traveling with a non-photographer, they will thank you for bringing a 24-105, instead of stopping and switching between three different lenses all the time.
My old 6D stood up well in rainy weather (I live in Seattle), so I wouldn't worry about that too much (within reason, of course...). During my 10-hour layover in London it was drizzling the entire time. I wandered the streets of London for 7+ hours with my 6D II + 24-70mm out the entire time -- no problem at all. Of course, the 6D II supposedly has improved weather sealing over the 6D, plus the 24-70 is a weather sealed lens, so do take that into consideration. I would not have done that with my 35mm Art or the 50mm 1.8 (or any of the pancakes), since they are not weather sealed.
The only factor that would change things for me is if you plan on doing birds or wildlife in Iceland, in which case the 7D2 + 55-250mm would be very useful.