Sisters (in laws) and brothers (in laws) are usually pretty easy to keep happy. They likely want to be a part of your wedding. If your husband wants to include your brothers in his wedding party you would be wise (VERY WISE) to include his sisters. If you are unsure have your husband talk to his siblings or his mother and see what the best idea is. If you can't include them in the wedding party give them another important job, a reading or handing out programs.
Fathers, Groom's dad's don't typically have a large role in the wedding. They are probably the person the groom goes to for advice, but as far as wedding planning I think they enjoy taking the backseat and enjoying the party.
Mothers, Groom's mom's do usually really want to be included during the whole process and including her as much as possible will really be to the benefit of everyone. Keep your mother in law involved by giving her tasks. Typically your mother in law (or her friends) may want to throw you and your husband to be a shower in her home town and will likely want to take the front seat in planning the rehearsal dinner. These events are really important to her and in general it is easiest and the best course of action to go with the flow. If there are parts of the event that you really aren't thrilled with (perhaps she's envisioning a larger rehearsal dinner than your wedding) talk it over with your fiance and if you guys really can't live with her plans than have him talk to her. Present your case fairly and calmly offer alternatives. In general be thankful. Remember she wants to show how happy she is for both of you!
If possible have your mother in law tour the venue with you and your mom. Ask her for her advice, share your ideas with her, take her for one of your dress fittings, ask her to come for one of the tastings. In my opinion most mother in laws want to feel involved. The more involved you keep her the happier everyone will be.
When things get sticky and sometimes they do it's important that you and your fiance present a united front. I think that usually each person knows the best way to deal with their families and therefore if you are having an issue with his family than it's better to ask him how it should be handled. If possible have him do the talking, if it's not possible than ask him how to talk to his parents.
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