You are correct, the will is not automatically invalidated because it has an interested party as a witness. However, you ideally will want a will that can hold up under scrutiny. You need two witnesses in Florida. I suggest that you use two uninterested parties as your witnesses.
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I agree-it is Ok to have one interested witness-but better to have two non-interested and notary(self proving).
You can get a proper will and peace of mind for less than $75 in many law offices.