I'm getting married in two months and I'm having a bit of a problem with my bridesmaids regarding their dresses. As all of my bridesmaids are different shapes and sizes, I picked a color and a length and told them they could get whatever dress they were most comfortable in as long as it was in that color and length. I told them this six months ago, and yet, as of last week, not a single one of them had even bothered to go look for dresses. Turns out that the color is one that takes longer to order, which has limited their dress selections quite a lot. My future sister-in-law in particular is throwing a (passive-aggressive) fit about it. I keep trying to explain to her that she needs to order a dress ASAP or she will not have one for the wedding, and she keeps putting it off because she doesn't like the options that are available after waiting so long.
And another of my bridesmaids messaged me and told me that she found the perfect dress, but it's a different shade than the one I asked her to get. She still wants to get it even though it's the wrong color.
I'm not sure what to do in this situation. I've tried talking to them and explaining the situation, but because we don't live close we rely on texting or messaging and they mostly ignore any texts I send about it. I feel like I'm annoying them because I message them once a day, but I don't know what else to do to make sure that this gets remedied.
Any advice?