Abeonis - thanks for your input.
I ended up using Sigil, which I am impressed with, and found easy.
I gave them a very detailed set of instructions, going through every step they needed. Unfortunately they just couldn't get it right, so I ended up doing it for them. Then they tried again on another book, but the same thing happened, and I had to help.
I'm not sure why they couldn't get it right, I know they tried. I think it was using the Sigil interface and some of the options that need to be set that was just too much for them.
So perhaps Jutoh would indeed be the answer for them.