You are not obligated to include your siblings in your wedding party. Keep in mind that if you do not include your siblings, you might very well end up being grilled by your parents or your siblings themselves as to why they are not included. You might want to make sure you have a good, non-inflammatory explanation. If you are going to include a sibling in your wedding party, you should probably find a way to include all of your siblings (if you have more than one). This might get unwieldy if you have a big family, but including all of them is really the only way to avoid hurt feelings. The exception is if you are only having a Maid/Matron of Honor and a Best Man. In that circumstance, you can probably get away with just including one sibling. If you are including some of your siblings in the wedding party but truly can't include all of them, find other special roles of honor for your other siblings -- have them do readings during the ceremony, etc.
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