Ask the wedding doctor
- do i have to ask my fiancees sister to be a bridesmaid if im not close to her
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Definitely not! You should not have anyone in your wedding party that you don't want or that you think you should have only because of obligation. This is not the time to 'keep the peace' and sacrifice one of the spots in your bridesmaid party that could have been filled by a near and dear friend.
Your fiance's sister probably wouldn't be very comfortable with the idea either, seeing as she is not very close to you.
This advice is not taking into consideration any specific cultural traditions - so if there is a tradition that requires you to have your new sister-in-law in the bridal party, you may be better off keeping to it. You don't want any nasty feelings to ruin your day and denying your fiance's cultural ideaology may start your marriage off in bad taste.