We have JUST started planning a wedding for next year, still no date, but went dress shopping yesterday with my fiance's two sisters. Over lunch, they asked about bridesmaids and without really thinking about it I invited them to be in the wedding party. Now after getting home and talking to fiance, I realize we only want a small wedding party (i.e. one close friend each). Can I phone up sisters-in-law and tell them I made a mistake when asking them? I think they will understand but I still feel like an idiot. Thx.
Usually, I would suggest that this would be very impolite. But, since you two are just beginning to plan and didn't really firm up budget, size, formality ... it can be done politely. Just tell them that you got caught up in the excitement and didn't think it through completely. And, as much as you would like to include them both, you two decided to have a smaller wedding and bridal party. Then beg them for their forgiveness.
It is best to wait for some time before choosing your attendant. Plans and friendships change.