First of all, I am sending you a cyber hug. It sounds like you are in a rough patch for sure. This profession attracts people who are kind and giving (you have to be!) and that means we are probably more likely to be people who have difficulty standing up for ourselves; however, we can learn! I would recommend you grab a cup of coffee and read through past postings. You will discover that the more experienced among us have all learned to grow a backbone, many through making mistakes early on. One thing I am glad I learned from this group before I began was NOT to accept families out of desperation, but to wait for a good match. It sounds like the three you have are a handful, so I hope you are able to find a couple of angels to counteract that.
In the meantime, you need to curb the 3 yo's aggressive behaviour. I have a friend dealing with a child like that, and I watch how she deals with it when we are at the park. The SECOND he shows aggressive, he goes back in the stroller for timeout. Some mornings, he spent the entire playtime screaming in the stroller, but over the 8 months I've been doing this, I've noticed a great improvement. I had one who had temper tantrums (4 year old) but I made her go into another room until she was calm, and I see huge improvement also. I think you need to find ways to take control of the situation rather than feeling like this is all happening to you beyond your control. As for the epi-pen, just ask for a doctor's note stating that he no longer requires one. You may have to terminate this child if you don't get it. You cannot afford to have a child die in your daycare! If you cannot do without the income, then perhaps you do want to look at other options, and there is nothing wrong with that. But you need to get the situation with the 3 year old under control. As for the micromanaging Mom, just smile and thank her for her input and then go ahead and run your business as you see fit. Crafts with a 15 month old... really? At that age it's you doing the craft for them. They can't even handle crayons without eating them....
Sorry to be so long-winded, but it sounds like you just have a difficult group right now. New children could turn everything around.