YES!The Christian Urich I'm looking for was married to Elizabeth Mosser!
Sallie's (aka Sarah/Salome) parents were Henry Urich (d. 1826, Rapho Twp., Lancaster Co.) and Elizabeth Baker.Christian had a son Henrich (b. 1766?), but I can't tell if Henrich and Henry were the same person or not.Dates don't quite match up, but they're not too far off.
Sallie Urich (10/8/1815-8/7/1876) was married to Jacob S. Haldeman.They lived in Rapho Twp., Lancaster Co., PA and later moved to Lebanon Co., PA.
Do you have anything that might help?
As far as the Brenneis mystery.My next guess is that my theory #1 was right - John Urich married Margaretha Brenneis and she died and he remarried Margaretha Volsin.But Margaretha Brenneis was the daughter of Valentine Brenneis as you indicated.Maybe Margaretha took over the care of her youngest two brothers when her father passed away, and that's why they are referred to as step-children?