Jackson is dismayed when his father hands him a kilt to wear to his wedding on the weekend. It’s a family tradition, and both Jackson’s father and grandfather were married in kilts, suggesting that the Belleville family have Scottish heritage. (Which made more sense when Jackson’s surname was Melville, which is a Scottish surname, while Belleville is French – although there is a historical relationship between France and Scotland, so it’s not unrealistic either).
I am not able to identify Jackson’s tartan – it looks most like a Buchanan Clan tartan, but I suspect it’s fictional.
Note that Jackson’s father is played by the real life father of Jackson Douglas, the actor who plays Jackson Belleville.