Florida law states that if you are in the state for over six months of the year, you need to register and tag the vehicle there. To do so, you will require PIP (as Florida is a no-fault state) and liability insurance.
Since your son lives in his own home at college, you will not have to add them to your policy if they drive your car less than ten times per year, with most companies. Some insurance companies offer a discount if you add a college student who lives away from home and has limited access to the insured car and seldom drives it.
While it can vary by your insurer, I would recommend getting your daughters' their own policy and simply paying the bill. Because you own the vehicles, you should be added as the additional interest to the policy.
If you're on your own policy without your parents, it's unlikely they would be sued if your coverage is exhausted after a car accident. Because you're considered an adult, regardless where you live, you would be sued if you were found liable - not them.