Weddingbee boards

Okay...my colors are purple, lavender and apple green...so I had a vision of my bridesmaids all wearing a different shade of dark or medium purple with bright green bouquets with a small splash of purple and lavender, my maid of honor wearing lavender with a lavender, purple and bright green bouquet and my 4 eight year old junior bridesmaids wearing lavender and carry lavender roses with just a apple green ribbon around their baskets. My daughter the flower girl would wear a white dress like me and have a lavender sash around it to tie her in to the flower girls...well I was all happy with that and even more happy I found a way to incoorporate the colors I wanted. Finally done...figured out. Now the nightmare...my sister one of my bridesmaids got my instructions on what color of dress to find and what color her daughter should wear,(she is a jr bridesmaid) I thought my requirements were pretty easy going. My sister and her daughter are are very over weight and I was having trouble getting measurements from her so I could have her dress made for her. She would procrastinate on telling me. So I get the call that she is getting the dresses made. I was so excited...until I found out she is getting a light purple dress(lavenderish) and she put her daughter in this flashy sparkly dark purple dress. Ahh! I am unsure what to do to tie the jr bridesmaids together now. I called trying to resolve the issue saying maybe they could just wear lavender sashes but I guess she did not like that idea. Should I just have them all wear different purple too with apple green sashes and have my maid of honor wear apple green sash too. My daughters dress is already being made with a lavender sash. I love color and bright shades but dont want it to clash or look like a circus. I am kinda...really freaking out. I am not superficial and I know shades of purple are not important I dont want my wedding to cause ill feelings for anyone. I kindly confronted my sister how I thought I was clear and she became quite angry and would not talk to me. So I caved. Like I said this wedding is not about colors. But I have little style awareness as it is and just need help with the whole situation. My wedding feel is peace and serenity I just want to keep the peace and come up with a solution that will work for everyone....PLEASE HELP ME!!

Thank you so much for the advice. It was what I needed to hear. My sister is unable to buy a dress in the store though because of her weight. I know her dress is tea length and chiffon so I will just ask my other bridesmaids to search for the same. My other bridesmaids are very sweet about things and said they will wear whatever I want them to. I just want to make sure they are comfortable in their dress (far as halter, strapless, tank or what ever fits them nice) and will wear it again. I really want the jr bridesmaids in lavender. I will just let her know. It is my once in a lifetime chance to design a wedding exactly how I want. Thanks again!