Precious childhood memories, illustrated with such a cute picture. Loved it, especially the bit about the sweet bribery. I'm Catholic as well, at least on paper. Nobody made us go to midnight mass when I was little, because my mom was a believer in young children needing their sleep.

Later (puberty) it was an excellent excuse for a young boy to get out of the stuffy family athmosphere late on Christmas eve and hang out at the local pub with my buddies. Back then, it was the law in Germany for at least one pub to be open in any given town to accommodate travelers and such. We would get to meet all those people who had to work on that special night - taxi drivers, cops, paramedics and what not - and celebrate with them. It was a most jolly affair.

Now, back to YOUR writing:

"...it starts from Dec 16 till either the 24th or the 25th. ... I'm guessing it's till the 25th cause if I remember it right it's being done 9 straight days."

So, you were entirely right on the start of it (16th) and on the 9 days - and now count with me: 16, 17, 18, 19, 20, 21, 22, 23, 24 = 9 masses, last one on Christmas Eve. Easily confirmed here:
https://en.wikipedia.org/wiki/Misa_de_Gallo

The midnight mass as such is celebrated by many Christians regardless of their faith denomination on Dec. 24, although not necessarily at the stroke of midnight. As far as your obligation as a believer goes, attending any of the Christmas masses (vigil and midnight on 12/24, or a mass on 12/25) is sufficient.

"It's possible that you guys have a different word for it."

Yes, they do, "kerstnachtdienst". Misa de Gallo is an Iberian tradition, the Dutch are perfectly content with a regular midnight mass:
https://nl.wikipedia.org/wiki/Kerstnachtdienst

Anyway, "Merry Christmas" to you and yours, and all the Steemians reading along :-)