[Phoenix]

At the end of the day, the system has to make sense to you. I am old enough to have used and abandoned many different numbering systems.

The one obvious problem with the system you suggest is that every direct ancestor can be described in two different ways. It would possibly be easier to list siblings, rather than children. Also, I don't have many families with more than nine children, but one ancestor had fourteen. Using letters provides compact flexibility. And when you suddenly discover a missing eldest child, it doesn't look quite so embarrassing.

My gut feeling would be to keep the system you already have for your father (possibly preceded with an F) and mirror that for your mother.

Unless you are extremely disciplined, the more likely you are to lose heart half way through, and have a system which is something and nothing.