Nurse ponies are not common even here where they were sold because, being at the end of the range, they didn't get a great distribution. Their hats are even worse because the pins break. So I would sell the nurses with the genuine hats one by one.
The replica hat in my view is something for individual collectors to decide on. For me a replica has no value so it would be just about which pony it was and how rare she is/condition - but other people might feel differently.
The Mountain Boys, it depends on their condition, since some are prone to regrind etc. I don't think your estimate for the complete set is necessarily out of the ballpark but I have seen Thundercloud sell as low as $30 on his own if he has damage...