Hey Nick-
I see a couple ways you could do that.
First and easiest would be to do the pork butts a day or more ahead of time for reheating the day of the party, and only focus on the ribs that day.
Next, you can overnight the pork butts, then when they're done wrap them tightly in foil plus blankets/newspaper and hold in a warm ice chest while you cook the ribs. You might be looking at a fairly long hold time if you cook your ribs at lower temps though and plan on serving everything at once.
Last, you could try putting both butts on one grate, and when those are in the last few hours of cooking use a rib rack to situate your ribs on the other grate. There is a post from Larry Wolfe a good while back that shows how you can fit an insane amount of ribs using a single rib rack. Cooking the butts and ribs all at the same time would personally be my least favorite option, since it is both the most hassle and the least likely chance of having all the food ready at once.
Pulled pork holds and reheats so well I would try to get those done ahead of time if possible, whether it's the day before or the morning of.
As far as whether or not it's enough meat, how many people you planning on? Is your son a hearty eater?
That's a good amount of food (especially with the sides), but it depends on how many people and what mix of adults/kids you'll have. Congrats on the big birthday... hope you guys have fun!
