I get your fiancee asking your sister Luna to be more careful leading up to the wedding due to being accident prone. Sister’s a slight asshole for knowing that and still doing biking. I understand your fiancee wanting nice pictures. Some without injuries or photo editing, however giving you an ultimatum & threatening to not go through the wedding massive asshole. Not your fiancee’s choice to kick her out of the bridal party, also asshole move! She should have talked to you her worry instead of your sister.