Don't look at it as single letter swaps, look at like a segment swap. ABcde and abCDE is the first swap. So the two connected/touched together or however you want to think about it at whatever point. Cut the strands and swap the alleles. Now move further down the chromosome and have another section connect/touch and cut strands, swap alleles again. That is kind of the mechanism but a double crossover is when chromosomes literally crossover each other twice. So the middle portion of the alleles swap the ends remain the same.
No, C is a triple crossover. You have 2 segments from each chromosome. You should only get 1 segment from the opposite chromosome and 2 from the original chromosome.