Steckelberg and Jirjahn are both documented in the vicinity of Dannenberg. The easiest first source is "Familienkunde der ehemaligen Aemter Dannenberg und Hitzacker" by Heinrich Borstelmann (Lüneburg: Herold & Wahlstab, 1938). Here are the entries for Steckelberg and Jirjahn:
[p. 155] Steckelberg: Brandleben 1709/10 Stoffer, 1/2 H.; 1727/28 Davied; 1749/50 Hinr. Chr.; 1799/00 Jürgen; 1929 1 H., auch 1 H. in Carwitz.
[p. 88] Jirjahn.
1727/28 Laase Hinr. Jirjahn, 1/2 H.
1769/70 (Jirjahn) Laase Julius Jürgen, 1/2 H. -- Hans Jürgen, 1/2 H., noch 1779/80.
1799/00 (Jirjahn) Laase Hinr. Joachim, 1/2 H. -- Joh. Jürgen, 1/3 H. -- Jürgen Ludewig, Pferdehüter -- Gr. Gusborn Joh. Hinr., 1/2 H.
1929 (Jirjahn) 6 Familien, darunter 5 Landw. 1 H. in Laase u. 1 Landw. in Gr. Gusborn).
Dieser in Nnds. früher sehr seltene Fn. ist ein wendischer und aus Jurjan, Jurij Jan (= Georg Johann) entstanden.
Now the interpretation:
The Steckelbergs came from Brandleben, where they are documented starting 1709/10. 1/2 H means owner of a half-sized farm. So there was a Stoffer Steckelberg living in Brandleben on a half-sized farm in 1709/10. And then a Davied (David) Steckelberg in 1727/28, Hinrich Christian in 1749/50, Jürgen in 1799/00. In 1929 there was also a Steckelberg farm in Carwitz. But I think you need to look in Brandleben.
The Jirjahns lived first in Laase. I think you can interpret most of the rest. Jürgen Ludewig Jirjahn was a horse tender. Johann Hinrich Jirjahn had a half farm in Gross Gusborn. In 1929 there were six families, among which five were farmers. One farm in Laase and one farmer in Gross Gusborn. The Jirjahn name, formerly very rare in northern Lower Saxony, is Wendish in origin and comes from Jurjan short for Jurij Jan, which is Georg Johann.
So you need to look in Brandleben for the Steckelbergs and Laase for the Jirjahns. The good news is that both were in the Langendorf parish, so all the church records are in Langendorf. They go back to 1729. There exists a cross-indexed marriage register for Langendorf, but it is held as far as I know only in the church office there: Alphabetisch-chronologisches Trau-Register der ev.-luth. Kirchengemeinde Langendorf der Jahrgänge 1729/1852, by Friedrich Biermann (Bergen/Dumme: Handschrift, 1971). This means that with some work and help from the Langendorf parish office, you should be able to research your families back to the early 1700s. Here is the address there:
ev.-Luth. Pfarramt
Elbuferstr. 96
29484 Langendorf
Germany
Now the interesting thing is that I have a bunch of data on the descendants of your Fred Steckelberg and his wife Lisette née Kohlmeier. I am related through the Kohlmeier side. Most likely you already have much of this data, most of which I received from Michael Steckelberg in 2001. If not, please let me know. Of course I am most interested in any Kohlmeier information you may have also, both ancestors and descendants. Also, my guess is that we may be related in the Langendorf vicinity, for that is where the Eggerts came from too.
Hope this helps.
=Jim