You are within your ratios, it really just comes down to what you are comfortable with. I have two children of my own (1 1/2 yr old and 3 yr old) and I currently care for 3 children full time and 1 child part time, and I'm looking to add another full time. The children I'm currently caring for are 1- 1 1/2 years old. I'm comfortable with this because my 3yr old goes to preschool two days a week for a full day and my pt child is here only two days a week, so I only have one day a week where I have to care for 7 children (once I get my other ft spot filled).

I think I would hold off terminating anyone until you decide whether or not you can handle all the children.
I'm not sure what the rules are regarding help, but I'm sure you can find info on the Revenue Canada site or something like that.