@mpass13 ...
Unfortunately, Canvas rubrics do not really allow you to make sub-criteria like you describe. You'd probably need to do some of your own manual adding of text to each criterion in your rubric...such as:
A. text
A1. text
A2. text
etc.
...or whatever you wanted to do. But, as far as I know, nothing would be indented within the rubric as a visual to let your students know that some things are a sub-set of the row above it.
Sorry I don't have better news for you...but maybe you can develop some kind of work-around that might be usable for your needs in your course. Good luck, and let Community members know if you have any other questions about this...thanks!