Vikings: I personaly think, the vikings havenīt use flaggs up to 1000 AC (when they become christians). The used some other things in my opinion. But its fine if you use the black raven for one of the viking nations ("Norway"?). For the other you could take the norman flag used by William the Conquerer 1066: two golden lions on red ground. Or some other norman flag.
Angel-Saxons:
Remember Merlin: Pendragon (Red Dragon) foghts against White Dragon. That means:
- Saxons: White Dragon
- Britons: Red Dragon (like the welsh flag)
Alfred, King of Wessex (871-899) used a golden Dragon as far I know. Harald fights against William the Conqueror 1066 by using a Red Dragon again.
Empire of Charlemagne: As far I know, there is no known flagg used by the Empire of Charlemagne. But the City of Paris used in 885 a "large saffron-coloured banner with large indentations carried by a double lance."... May be, you could use the William the Conquerers flag (look above) here. But sure, itīs a norman flag...
If you find nothing more, you could take a White Cross on red field (for "Germany", like the danish flag today) and White Cross on blue field ("France"). It is not historical correct, but these are the earlyest flaggs I know for this "nations".
Hope you find some more detailed informations. If not, I have somewere images some of these flags, I could send it to you. (if I find it again).
AroSch