Well I think its the perfect set up ... Your not tied down all summer and you still make some money ..... And if you lay down he law with these kids right away with regards to behaviour. Being a blended family is different in the sense they get a break from each other every other week. I guess for me it would depend what the ages are. In other words are some of them close in age (with each other or with your kids) so they have a friend to play with or is it going to be too hard to keep them all occupied .....however it is for only four or five weeks total.
Yes I would ask for at least a one week deposit (applied to the last week(s) if care and a holding fee (non refundable and only holds the spots) for may and June otherwise I would continue to advertise. My holding fee is $250 / month.... Not sure what I would do for four spots in the same family .