Just to clarify, while your parents may in reality be your dependants, even for tax purposes, they do not qualify for TD, which is reserved for spouse and children.
There is a 'partner B2' which would essentailly be an extended B2 status, but this would still require maintaining a foreign home at all times.
So, they can at best 'visit' you.
They enter for 6 months, with or without I-94, in B2 status. They don't 'live' in Florida, they visit.
Your parents will get 6 months status (or visa if the are not Cdn) and will do the same, without any problem. Why are you worried about this?
It's just that they will not be able to give up their foreign residence, which TN/TD are allowed to do.