Six Month olds High-Pitched Screaming

Dear Naomi, I have six month old twin girls. They are breastfed, we co-sleep, and they are given as much loving attention as possible. I do my best to naturally, attachment parent them, but it is difficult with two high needs babies. My husband is just establishing himself in a demanding industry, and works odd, and long hours. We have alot of help from family members; my mother has basically given up much of her own life to help us. I also have aunts and cousins who help sometimes--I am fortunate. Everyone is giving as much of themselves as possible. Despite this, the girls have recently began screaming at ear-piercing, headache inducing decibels. They do it when they are stressed, when they are happy, when they are tired, when they are in the car, etc. It is beyond tolerable for anyone within earshot. I have no idea how to communicate to them at this age that it is not ok. I have tried discouraging it by immediately giving them a pacifier, which often works in the short term, but thats it. (A note on the pacifiers: they spent time in the NICU after birth, which is where they were given them-this was not my choice, and because I am not able to breastfeed them both as much as it would require to fulfill their sucking needs, I see no alternative, but to continue to allow them for the time-being. They are used as sparingly as possible) Possibly significant history FYI: They had a very traumatic birth; including epidural, emergency C-section (although the one who suffered the most trauma has turned out to be much more easy-going than the other, super-sensitive baby), and then they were separated and put in incubation for growth within hours of their birth. They were kept there for 5 days; I was with them constantly, day and night, but was recovering from my own trauma as well, and have alot of guilt about not being there as much as I would have liked because I was simply, physically incapable. They are being treated with homeopathics and cranial-sacral therapy, but I don't think there is anything that could replace being with me for those first crucial hours and days. Please, any suggestions for this issue would be greatly appreciated, along with any other general advice re. parenting twins you may have...please help before we are all deaf!