Continuation from the earlier message.
Unfortunately the birth index for the years around 1900 when your grandmother was born is not accessible. Also not accessible are the birth records themselves from 1860 onwards. However, there is the birth record of Michael Christl who might well be an elder brother of Rudolf. This record says:
Birth of Michael Christl on Sept. 29, 1859, at house Kollerschlag 76.
The parents are Michael Christl, cottager, and Barbara, daughter of Thomas Balzer, cottager at Artschlag?, parish of Mei...schlag? in Bohemia, and of Barbara nee Fischer.
This record in the original matrikels has a very important marginal note (which the duplicate record likely will not have) about the marriage of Michael. The note says that Michael Christl married on January 20, 1908 in Alcoven. His bride was Maria nee Haslinger. Alkoven must be the town with this spelling south of the Danube and close to Linz.
There is another marriage record of interest which dates to earlier times.
Marriage on January 26, 1814.
The groom was Paul Christl, farmer and weaver, age 26, the son of Paul Christl, cottager and weaver in Schönau, parish of Wegscheid in Niederbayern, and of Maria Anna nee Hag.
The bride was Katharina Rauscher, age 24, daughter of Leopold Rauscher, retired farmer in Kollerschlag 39?, and of Maria Anna nee Rauscher.
There are other records I had no time to look at. Unfortunately, the two Pauls (father and son) and the two Michaels can hardly be in one direct line, but their Christl lines could be closely related. Much more is to be found for you. Good luck.