I think you need to be looking at professional software, and probably need to register with the IRS as a tax preparer.
The desktop version of Turbotax can prepare 80 returns, but the last 75 all have to be filed by mail. And they have to be signed by the taxpayer, because even if you have an IRS registration number, it is a violation of the regulations and the turbotax license for a preparer to sign a Turbotax return, since it is supposed to be a personal use program.
