In the novel I'm writing, there are two characters who are meant to come off as less intelligent. One of them is a woman who was born to a nobleman father and a mother who comes from a wealthy family, so even though she's educated in things such as literature, art and philosophy, she lacks real world experience. In the story, that manifests itself as her being a horrible judge of character (believing everyone she meets is a good person with her best interests in mind), not forming her own critical opinion but accepting what the people around her tell her as facts (i.e. she supports everything Mussolini does before and during WW2) and going to great lengths to not be seen as a bad host, even when the character who's in her home is being an awful guest.
The other less intelligent character, who I'm having more trouble writing, was born on a small island which he didn't leave until he was forced to join the war effort as a soldier. He was a fisherman before the war and didn't have any formal education whatsoever. He has no understanding of the complex politics surrounding WW2, but he does understand what's happening on a smaller scale (e.g. the people he's escorting to a boat will be transported to a concentration camp where nothing good will happen to them). I'm having more trouble expressing his lack of intelligence than the above mentioned female character, maybe because with her it's more that she's naive than outright stupid. So far, I've come up with him calling his comrades from the army his "friends", even the ones he hates, and I've made him not understand a joke that someone told.
How do you write characters who are less intelligent than you, and more importantly, how do you make them sympathetic enough that the reader cares about what happens to them?