I had just reread volume 8 of the series. There are a couple of panels where Negi's Uncle is seen in. The two panels are on the bottom of page 53. In the largest panel, Negi's Uncle and Nekane's father is the man pointing to the location of the demon attack on the village. He is seen in the small panel on the right side of the page.
After I read Volume 8, I am beginning to think that the Springfields are a powerful Magi Clan. Negi's father is claim to have the ability to magnified any spell a thousand times. Hence his nickname "The Thousand Master." All I can state that Nagi is a very powerful Combat Magi. He does have his share of enemies. One of Nagi's enemies was behind the demon attack on Negi's home village.
Throughout the series since Volume 1, Ken had to include clues which disclose some facts about Negi's family. One of those clues may have been disclosed in Volume 8. Negi seems to belong to one of most powerful Magi Clans. NeKane's father is likley a village leader since he seems to leading a party of magi during the demon attack on the village.
We don't know much about the family of Negi's mother. I do believe that Nagi Springfield loves his wife. What he was doing before his disappearance is only limited to Asuna's dreams. If the Princess of Dusk turns out to be Negi's mother, this means that Negi is a real life Prince.
The Princess of Dusk will appear in Chapter 169. All we see of her is that she is to her back, and flying away with her cat-bat like partner.
Susano
: