I think you've over-styled yourself into a corner, here.
We've found that no styles works best.
1. Make a copy of your project and find a default.css from
the RoboHelp Office > RoboHTML folder (under Program Files).
2. Assign the .css file to a few topics with these nested
lists. In the topics, remove all styling in the lists (down to
Normal paragraphs, no indents, etc.).
3. Select all list items from a former nested list and click
the RH
Create a Numbered List toolbar button.
4. Select the sub-list items, click the
Increase Indent toolbar button, and adjust the numbering to
a,b,c. (To automate this part of the process, you could add a "OL
OL" style for only the a,b,c format [no indents, etc.]).
5. Repeat steps 3 and 4 for all other nested lists in the
topics to which you assigned the default.css file.
We've found this method the most pain-free way to achieve
consistency in online and print output. Give it a try. Or...you
could step1/step2 yourself all the way into therapy.
Good luck,
Leon