How to use the same category group as a filter on multiple channel sections?
I would use a dynamic route instead of the path and template assigned in the category group. If you want the urls to be /Steve/B and /Bob/B, the route would look like {tag}/{slug}. Then in the template, fetch the channel using tag, and the category handle using slug.

Fetching the category:

{% set category = craft.categories.group('categoryGroup').slug(slug).first %}
{% if not category %}{% exit 404 %}{% endif %}


Fetching the entries:

{% set myEntries = craft.entries.section(tag).relatedTo(category) %}