I understand this use case pretty well, actually, since I'm helping my father with a book. And since I'm a Leanpub cofounder, I have a lot of tools here.
Frankly, however, I think the following low-tech solution is the best approach:
- Have your parent make their own account, which is where the actual book will be published. This can be a Free account. It presumably won't preview or publish more than 10 times a month. Make the real book be a Dropbox book. If they want to credit you, and you want to be credited, they can add you as a collaborator. Or you can just be the uncredited tech support. As some comedian pointed out once, they taught you how to use a spoon, so you can help with the computer!
- Make a stealth-mode book on your account where you can work on the manuscript. Make yourself the primary author. If you wish, you can invite them as a co-author. This would also be a Dropbox book (if you're working on it together with them as a co-author), or a GitHub book if you're a programmer and you're just going to do it all yourself. There are two reasons to make it on your account: first, if you have a Standard or Pro plan you have unlimited previews, and second, you can work on the book and preview it as much as you like, without them seeing the previews and asking questions or feeling like an imposition. (In that case, you wouldn't invite them to be a co-author.)
- Set a custom name on the book, so that your name doesn't show up on the preview. To do that, go to Author > Books > (the stealth mode book) > Book Info > Authors, and click the "Edit Your Author Information Shown On This Book Only" link.
- Do all the previews and publishes on the stealth-mode book, to get the manuscript right.
- When you're both happy, just copy the manuscript into the correct Dropbox book on your parent's account, and have them publish it.
This may sound complex, but I honestly believe that copying files is simpler and will result in less support work for you (or for us!) than managing roles and permissions would.
The only real issue is that the verso page of the book you are previewing will have the URL of the stealth mode book in it, not the URL of the book on your parent's account. So, if they want to share the book with someone, just copy the manuscript to their book, have them do the preview.
Also, this is not what our publisher program is for. We're overhauling our publisher program sometime in the medium term, possibly in the next year, but it's not going to be for this use case then either...