Are you sure there isn't a medical reason - like even constipation for this behavior? If it is painful for kitty to go to the bathroom, they often associate this with the box and will stop using it. If his poop seems very dry, consider adding wet food to his diet if he doesn't have it already. Consider purchasing a drinking fountain for the water (like a DrinkWell fountain).
Also, the rule of thumb is that you should have one more litterbox than you have cats. I'd add a third litter box. And if they like the larger box - maybe even consider just replacing the smaller box with the larger one. Maybe Asher would use it if he felt more comfortable - and he only likes the larger one, but Jack already used it or something. There's no way to "assign" boxes to cats. Asher and Jake don't know that any litter box "belongs" to either one of them.
You can also consider purchasing an automatic litter box. We bought ours when we had money (wouldn't be able to afford it now) - but the Litter Robot is FABULOUS (but expensive). http://litter-robot.com/
. If you decide to add an automatic litter box, place it next to the one they're using for several weeks before you remove the non-automatic box.
Our cats sometimes attack each other coming out of the box - so placement of the boxes can be VERY important to kitty feeling comfortable using a box.
We have six cats and eight litter boxes (two of them are automatic) - and there is at least one litter box in every room of our house (except the two bathrooms, the powder room, and the kitchen).
The only time we've ever had a litter box problem is when there's a medical problem.
If you're worried about people seeing the boxes in places other than the laundry room, perhaps you should consider litter box furniture? Example: http://www.hidytidy.com/
Hope these ideas help,