Litter box math is important. Very simple equation: 1 litter box per cat + 1.
A litter genie (like the pail you linked) is a great choice for building the habit of cleaning the litter box often. Recommended to keep one near each litter box.
Also be aware, pine bedding can be an irritant to humans and cats (and many other mammals). It’s usually not recommended— mostly due to the dust. Pine pellets tend to be more safe due to how they’re processed.
Be wary of canned tuna- it tends to have higher levels of mercury which over time (such as daily feeding) can cause heavy metal poisoning in humans an and small animals. I personally don’t even bother, my cat gets freshly cooked shreds of meat as treats once in a while and special occasions.
On the topic of training: be patient, don’t use a water bottle or snap / loud shouting. Instead, when they’re doing something they shouldn’t be, calmly pick them up and physically move them to somewhere they can be and provide a toy or activity to replace the thing they were trying to do. Such as a string toy or other floppy toy out in the open if they were caught playing with computer wires under the desk. This goes for scratching too, if they are scratching the door/couch/bed/carpet, etc— place cardboard or rope scratching posts and pads nearby and physically move them from the bad spot to the good spot. Move around the good spots as needed based on what you observe. You will have to do this a lot, generally, but be patient and they will get the message. Positive reinforcement includes those toys and scratcher, you don’t have to provide a treat every time, especially as they grow up and become more independent.
Sonic Adventure will always hold that special place in my heart. It was just so amazing then. And the chao garden + VMU integration!