If he is filing a tax return as single, and can claim himself as a dependent*, then he can convert ~$10k/year without paying any federal income taxes. He might have to pay state income taxes, so check local listings. He should be able to do this within 4 years at that rate, and once in the Roth it should grow and pass on to heirs tax free.
* Since his children will support him, they may expect to claim him as a dependent. That would change this scenario a bit.
