Based on the invasions in your videos Soba is more laidback and just wants fuss and attention, while Udon is more playful and mischievous. Is that accurate, or are their onscreen portrayals deceptive?
Their onscreen portrayals are accurate, but I would describe them both as playful and mischievous. They can both be laid back if they want to, but much of the time they are Fast and when they're Fast they are Dangerous and Difficult. In many ways they are the same cat, it's just that Soba feels more like she's actually in the room with you, while Udon seems to be some kind of mercurial, transdimensional being with one foot in another universe.