I hope this message finds you well, present circumstances excluded. I am a licensed attorney with over a decade of employment law experience. It is a pleasure to assist you today, though I am sorry that you are having to go through this issue.
Based on what you have shared with me, the advice of the two Florida lawyers is likely correct. That said, in attempting to prove that your husband was not a simply 1099 contractor, you need to be able to put forth evidence, anything you can show, that he was beholden to this client and his father, and therefore did not have autonomy as would be the case with a contractor. Contractors maintain some degree of autonomy in their endeavors relative to employment You may be able to compare and contrast the previous job he held at the academy with the work he did for these people. In essence, he left one full time employer, that maintained control over him and his schedule, to work for another full time employer, that likewise maintained control over his schedule.
The meat of this will be showing that your husband did not have autonomy as would be the case if he were a contractor and being able to show that he had not other jobs of similar nature.
One other issue, though I am not sure it is worth pursuing in the immediate present, is that this person covenanted to you guys that your husband would be paid for August and September and then recanted. This is arguably a verbal contract and you could sue for that money. You need only show offer, acceptance and consideration (that you guys relied on this guy's word to your detriment). That suit can wait while you handle the immediate issues, but it is likely there for the taking if you choose once you get squared away financially in the present time.
So, in summary, you need to be able to show that your husband was exclusively beholden to this man and his son. This can be showing texts, emails, sworn statements you guys sign, etc. It can be shown by check receipts or deposits of the same amount month after month.
Let me know if you have any other questions.
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Best wishes going forward!