i won't say that it is uncommon for a widowed sister-in-law to marry her brother-in-law, but in the present saga -- it definitely is preposterous -- esp. since they have shown the relationship between Karan and Urvashi to be purely platonic!!
This only re-inforces the widely accepted and convoluted belief of most people that there can never be a platonic friendship between men and women. Sad that the makers and writers of this otherwise good soap think this way too.