As far as I can see, there are some ongoing track works at Hürth-Karlscheuren. But according to zuginfo.nrw, this should only apply to RE12, RE22, RB24 (trains going from and to the Erftstadt/Meschenich direction). The tracks and trains from Brühl and Bonn are not mentioned in this.
In normal times, trains that are visible on bahn.de or in the Bahn app are scheduled. But there might be some late-minute problems and changes to the timetable.
And about the 9 Euro ticket: It is also valid on local busses and trams! So buy one for each family member and hop on every bus/tram/local train you want.