Van der Gaag - Hoeks Family Tree

vulgo (latin for commonly) Heidler Johann, perhaps fathers last name?

According to the wikipedia of Kaisersteinbruch, Kaisersteinbruch was not a single quarry, but multiple.
I quote from this article: https://de.zxc.wiki/wiki/Kaisersteinbruch

"The Kaisersteinbruch is not one quarry, but several depending on the order situation. In 1901 and 1912 technical data were collected for the Buchthal break, the forest break (Ödenkloster break), the chapel break, the house break and the Teuschl break. The following were also mentioned: Zeiler break . Pansipp break, Amelin break , Kaiserstein break, Blauer break, Black marble break, cavern break and Winkler break, as well as old Teuschl break, society break, Kowel break, Theresien break, salt lick break and Cobalt Break. A contemporary report can be read: “ The small town is completely surrounded by quarries and its houses are almost completely undermined. ""

According to multiple sources (baptism and lexikon), Johann was working at the forest break (Ödenkloster break).

In the time that Johann worked there, the quarry was owned by master stonemason Ferdinand Krukenfellner.

According to his Wikipedia page (https://de.wikipedia.org/wiki/Ferdinand_Krukenfellner), the quarry delivered stones for the "Vienna Ringstrasse" court opera, the court museums, the Hofburg on Michaelerplatz , the town hall. Since Johann was of a working age when these buildings were made, it would be fair to say that Johann helped building these impressive buildings.

Second name: Nep.

"Nep might be short for Nepomuk, after https://en.m.wikipedia.org/wiki/John_of_Nepomuk

He was a popular Saint, and giving your kid a longer name is one way to differentiate him from all the other Johanns in the parish"