Hi J.,
I don't know if this will help you, but here's what works for my very, very distracted first-grade son...
I should preface this that even with no siblings, when we tried doing homework with him at the kitchen table (while I did dishes, or even sitting with him to keep him on task), he'd get very distracted. We have a big picture window right next to the table, so anything going on-- a car passing, birds flying into the backyard-- he was immediately off task.
This year, I made a place for him in the less-exciting dining room. Our table in that room is rarely fully used (it has drop sides) so it is like a desk against a wall, and his seat faces a mostly-blank wall. Visual stimulus is limited. He does better here and completes his work more quickly here than when he chooses another place (I offer him the choice, so long as the work is done). We keep music/tv off, so there's minimal noise. I might sit next to him with my laptop or read a book, because he does seem to need company some days.
If you want him closer, is there a place where he could get set up out of the main traffic area and use a cardboard study carrel? Here's a homemade one--
http://spoonful.com/crafts/homework-central
I personally would not have so many things in the visual field. My son has a visual dysfunction which renders that many items to be distracting. All of our pens/pencils, rulers, markers etc. are in a basket on a separate table to eliminate visual clutter.
I'd also suggest using a timer to keep him on task, too. Like "you can work on your illustration for 5 minutes" then check in, state the next task and set the timer. My son's teacher does this with a few kids who need help managing their time. Ultimately, it depends on how much help he needs with the homework, I think.