Hi there! First of all, last three weeks have been pretty warm here in Finland. Temperatures have gone up to +32 C on day time in shadow, making this - at the moment - hotter than Germany. Next week though, major rain is expected in the beginning of the week (28th, 29th) so I can't just yet tell how it will continue. Be advised that this is the major summer vacation month generally in Fennoscandia.
So, what do you expect to do around here? In Germany, I believe that will be more about sights and relatives, so I guess 28-135 or 24-105 would work best. Here it's a bit different. Since I don't know where your relatives spent their summer time (could be a summer cottage or a city dwelling), this may affect your lens choice. Sun sets around 23.20, and will rise around 3.30 in the morning in my latitude. This means you don't practically need large aperture lenses for getting more light in July unless you go to dark places like house interiors. And also that the moment of golden light will last considerably longer. Typically, it tends to be not possible to see stars until September.
Staying in a summer cottage and general waterscape around it may push your choice of focal length towards the extremes. 28 or 24 should do fine for wide-angles, but you'll be lacking there if the longest focal is 105 mm when photographing sunsets as occasionally longer telephotos work better there. However, I think that the 24-105 itself should work pretty nicely for almost anything if you absolutely want to carry all-in-one package.
Personally, if the weather remains as it is now, I'd seriously consider taking a point and shoot. Even carrying a 5D and the small EF 50/1.4 sounds like an annoyance in +30C to me so if I had to take a 5D, I'd go with a 50 mm prime. But that's simply because of the weight and temperature, but that's me. If the temperature drops to +22C, then I'd have no qualms of taking another lens with me. When I was in Canary Islands a couple of years ago (in November), a combo of 28/1.8 and 85/1.8 worked well, though even those two felt heavy after carrying them the whole day in a camera bag dangling from the back of the neck.
Traveller Gear insurance is mainly needed for the possible damage that you'll encounter in the luggage handling. Other than that, there are practically no street pick-pockets and I have never heard of anything being stolen from a hotel room here. Of course, you shouldn't leave the camera unattended to a bar table, or leave anything of value to a traveller's hostel where rooms are shared, but hotels are a different game. In Germany, it's pretty much the same.
