Pictures would help showing both the plants and where and how you are growing them. Without that, all I can say is 9 out of 10 times lavender dies, it's due to an issue with too much soil moisture. You could be watering too deeply, too frequently, or the soil isn't draining fast enough. The Moisture Control mix is not a popular choice because it has a substance added to it that serves to retain water, which is the last thing you want with lavender. Also, I don't know your reasons for adding all that to the potting mix, but at the least it isn't doing any good and could be making things worse. Lavender likes quick-draining, sandy to gritty growing medium with a slightly alkaline pH and low nutrients, and all the sun/heat they can get. Something like a cactus/citrus mix might work. For more information on how to grow lavender,this website is has good information (just ignore the silly background).