The tax returns may be helpful to you, as a "relevant document" showing evidence of your presence here on certain dates, but may not be considered sufficient proof by themselves. School records or employment records would be better for that purpose.
Those tax returns could be a problem for your dad, though, depending on your country of origin. He cannot claim you as a dependent unless you were a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico, and met all of the other requirements for a qualifying child or relative. If he claimed you incorrectly, he could owe additional taxes for those years.
These answers are provided for educational purposes only, and should not be construed to be either formal legal advice or the formation of a lawyer/client relationship. For specific legal advice that applies to your individual situation, you must be a client of this law firm.
you ought to consult with an immigration attorney regarding the evidence you need to qualify for deferred action. Generally, tax returns and tax documents may be helpful evidence, but may not be conclusive in themselves.
This information is provided for educational purposes only, and is not to be relied upon as legal advice. You should consult with an attorney with full disclosure of all facts and opportunity to consider all or alternative options.