I called the local ATF branch yesterday and spoke with one of their agents.
He told me that here in Missouri, Charles can not even hunt with a muzzle loader, but if he lived in Kansas he could.
Suzy can own all the firearms she wants. But, like most of you said, she needs to make sure he has no access to them. The recommendation is to have Suzy keep them at a friends house.
He went on to say that normally there would not be any problem, but if Charles ever had a serious run in with the law again, they might go digging around and use any firearm in the home against him.
His final statement was "Why take the chance?"
So thanks for all of the replies and the info you provided. Seems most of you either work for or know what the ATF rules are.
Good Job all!