Is it customary to invite your fiance's sister to be a bridesmaid? The simple answer is that you are not required to include anyone, even a family member, in your wedding party.
If you decide not to have any bridesmaids or ushers, then your brother-in-law or father may be able to help out with a role during the ceremony or reception. They could be given duties such as holding a door open for guests, or standing in for an usher at certain points during the service.
It is also acceptable to have only male ushers or no ushers at all. There are many ways to customize your wedding party so feel free to discuss different options with your fiancée and allow them to suggest people they would like to be included in the wedding party.
As long as there are no hard and fast rules, you can do whatever you want with your wedding party. As long as you both agree, someone from each family can be included in the wedding party.
Is it necessary to ask your fiance's sister to be a bridesmaid? According to Sharon Naylor, author of "The Bride's Diplomacy Guide," it's preferable to make every attempt to involve his siblings for the sake of family unity (Adams Media; 2007). Don't even think about it right now. She'll just feel excluded and that will cause tension between you.
It is best to ask permission before making her a bridesmaid. If she doesn't like the idea, there will be trouble ahead. Your fiance's sister may have her own ideas about who should be invited to what role at the wedding so be sure to discuss it beforehand. If she has suggestions they should be respected.
If she agrees to be a bridesmaid then thank her by including her in important decisions such as this one. Ask her what kind of dress she would like to wear on the day and if there is a particular theme you should follow during the ceremony and reception. Inviting her fiancé's brother to be your best man can also be an appropriate gesture. His opinion and input will be greatly appreciated by both you and your fiance's sister.
Finally, remember that this person is part of your family now so treat them with respect and affection.
There's no law that says you have to make your sister your maid of honor or involve her in your wedding party at all. Of course, leaving her out runs the danger of sparking a schism, so if you and your sister are on good terms (or at least have a semblance of it), making her a bridesmaid is strongly suggested. However, if you two are not getting along, having her serve as one of the flower girls can help bridge the gap.
Also worth mentioning is that while men usually have their friends act as their best men, this isn't compulsory. If you don't want your brother-in-law or other male friend involved, they will understand.
Finally, there's no rule that says you have to include your sisters in these decisions. If you want to make your wife/girlfriend a part of some but not others, that's fine too. Just because she's your sister doesn't mean you have to share everything with her.
And nothing prevents a bride from appointing her brother as a bridesmaid or a groom from appointing his sister as a groomslady. While you may not need your bridesmaids or groomsmen to help you plan your wedding, there will be times when you will need to know you can rely on them. For example, if one of your bridesmaids is in charge of planning the wedding breakfast then it's important they have enough volunteers to cover for them if they don't show up.
The most common appointment is for the brother or sister to serve as a witness to the marriage. If this is what you want to do then be sure to ask your pastor or priest whether this would be acceptable and appropriate. Sometimes other family members are invited to attend the wedding but not allowed to give testimony - for example, the father of the bride or groom might object if any relatives were allowed to serve as witnesses because they might feel excluded from some of the special moments during the ceremony.
If you want to appoint someone else to act as a witness instead then this person should be able to testify as to what happened on the day without violating their privacy rights. For example, a best friend could serve as a witness if the couple wants to keep this information private until after the wedding.
It's also acceptable for the brother-in-law or sister-in-law of the husband or wife to serve as a "giving witness" during their wedding reception.
While there is no requirement to invite your soon-to-be in-laws at the wedding party, omitting them might lead to broken emotions if you are not careful. They may feel excluded or unimportant.
As far as what to do, if you want to invite your in-laws then by all means, invite them. However, if they make you feel uncomfortable then it's best to keep them away from the ceremony and reception. This will give both you and your husband-to-be time to get used to being married without having to worry about their feelings.
It's also important to note that the bride's family has no control over who joins the wedding party. So if you have strong feelings against having your sister-in-law in the wedding then you should probably just say so now before it's too late.
Finally, remember that this is your day. You can invite whoever you want to be in your wedding party and it doesn't matter what role they play in your life. Just because they're related to you doesn't mean they know you well enough to make an informed decision about who should be at your wedding.
So, as long as you don't have any major issues with your in-laws, you should be fine inviting them to your wedding.