Caroline Louise Dorothea Bernberg is the grandmother of your grandfather Christian Jepsen Christensen. (That's an informal rendering of her name). Christian married your grandmother Mette Kristine Nielsen, as you said, and it is interesting that Mette's family also migrated from northern Germany into southern Denmark. Mette's father was Niels Peder Nielsen and Mette's mother was Cecilie Marie Nielsen. I believe this is Niels Peder and Cecilie when they were newlyweds:
Ribe, Gørding, Vilslev, Jested By, Et Hus, 39, FT-1880, D3701
Søren Nielsen 58 Gift Husfader born in Jested, Vilslev Sogn, Ribe Amt
Mette Nielsen 50 Gift Husmoder Toste, Slesvig
Dorthe Marie Nielsen 10 Ugift Deres Barn b Jested, Vilslev Sogn, Ribe Amt
Niels Peder Nielsen 22 Gift Slægtning b in Beis??, Slesvig <--
Cecilie Marie Nielsen 22 Gift Slægtning born in Vester Torp, Slesvig <--
Gramtrans translates "Slægtning" as "Relative."
Ribe, Gørding, Vilslev, Jedsted by, 7, Huus, 142-F2, FT-1890, C1925
Niels Peder Nielsen, 33, Gift, Husfader, Arbejdsmand i Landbruget, born in Nordslesvig
Secilie Marie Nielsen f. Mamsen??, 34, Gift, Husmoder, born in Nordslesvig
Søren Kristian Nielsen, 4, born in Vilslev sogn Ribe amt
Mette Kristine Nielsen, 2, born in Vilslev sogn, Ribe <---
"f. Mamsen" means født Mamsen, born Mamsen = her maiden name
LINK to 1890 census:http://www.ddd.dda.dk/asp/vis_husstand.asp
LINK to that online family tree, showing Cecilie Marie Mamsen:http://www.gloggengiesser.dk/tng/getperson.php?personID=I165...