I'll try and connect you with someone who can help. But frankly, I would teach them to do it on paper. Until you get into running a small business or some of the odd deductions and credits, a basic tax return should be easy for anyone to do on paper and it's a shame more people don't try. The IRS publishes scenarios in their e-file instructions that companies are supposed to use to validate the software results, you could use some of the simpler versions of those.
Or contact the IRS or VITA.