It does sound like there is some benefit form it.
As for ow long it lasts, that depends on the child and the dosage. Our pediatrician showed us by drawing a graph of an upside down parabola with a horizontal line cutting through it above the X-axis (if that helps). The horizontal line is the medication blood level needed to produce a benefit, when the parabola isbelow that line, you can't see any change. As the parabola goesabove the horizontal line, you see them quieter, calmer, better able to focus. The height of the parabola is the blood level of the drug. The width of the parabola is how long-lasting it is. But you can also see, with something that is sustained-release like Concerta, the parabola has to be fairly wide. But if the dose is still too low, or the child's horizontal line (varies for everybody) happens to be set higher than average, the wide parabola will dip below the line too quickly even so.
The outcome is - the Concerta could well be working, but wearing off too soon because the dose is low (for him). There are several ways of dealing with tis, and it still involves thinking about the paraola, plus observing your son to try to develop his own graph.
What you do, is observe. How is his ability to focus? When do you notice him beginning to have difficulty? When you DO notice this, is there any hint of rebound? Or is it just a return to normal? (I hope for your sake there is no rebound, because it sounds like the Concerta IS working).
If it's wearing off way too soon, say midday, then eiter the dose needs to be increased at the begining of the day, or he can have a second dose at, say, 11 am, or he could get a top-off dose of ritalin (short-acting) after lunch. You have to be careful to let the blood levels drop to below the horizontal line by bedtime (usually earlier) so he can get plenty of sleep. Also, these medications tend to suppress appetite so if the levels drop low by dinner time, then he is more likely to eat a good-sized meal and this helps counteract the appetite suppressant effect.
The aim is to keep the parabola with a shallow curve above the line for the time of day he most needs it (during school hours, at least) but below the line first thing in the morning and last thing at night. Of course, this means we cop the worst behaviour at home, and often at the end of the day when they're also dealing with the accumulated stresses and fatigues of the day (and so are we). We need a bucketload more patience at the end of the day to deal with this, we also had to learn (in our house) to go easy on punishing then because the kids were just not able to keep it together at the end of the day. That's when I learned to shove food at them when they got home from school (medications worn off by then, but they were also exhausted and would soon be too tired to eat) and put tem to bed early, until they got used to it all.
Homework is usually a huge issue, because they really concentrate hard all day at school, then they come home, with medications wearing off/worn off and are expected to do more! Frankly, if it's a problem you need to talk to the school about lightening up on him, or perhaps setting work than can be done one day on a weekend, during the day when he's medicated. It's not fair to the child or the family, to expect a severely ADHD kid to do homework midweek. Also, increasingly the research is coming in saying that doing homework doesn't increase the academic standard long-term. Coaching is different, it does raise the academic level to a certain extent. But homework - no.
With the oppositional problems, you have several issues here and you need to do your utmost to nip this in the bud. And you DON'T stop it by getting just as oppositional yourself. Firmness doesn't stop it, it makes it worse. Read "The Explosive Child" by Ross Greene, it really helps a great deal.
For tidying up, a tip of mine - ask them to pick up ten items and put tem away. Also be aware, a Pervasive Developmental Disorder (PDD) kid generally has trouble with transition. So if he's putting that model together, and you call him to wash his hands for lunch, he will either ignore you or loudly refuse. But if you say to him, "Lunch will be ready in fifteen minutes. Get yourself to a point where you can put that down, then go wash your hands for lunch," you are more likely to get cooperation. Standing there tapping your feet wouldonly heighten his stress and make him more argumentative about it, you need to lead him from task to task.
With the tidying up, I found that if I got him to work alongside me, we got a lot done. We then did something HE wanted together, as a reward. Or I use bribes (freely). For example yesterday, "difficult child 3 - I need you to empty the dishwasher and then put a loaf of brad on to cook. When you've done that, I will take you to the beach. We can go as soon as those tasks are done."
I sometimes add, "While you're doing that, I will be doing the washing." That way he knows he's part of a unit, and not feeling like he's the only one working.
The floors - I'm not sure what you can do there. Are you sure that the floors can't take too much? A dance floor (sprung floor) certainly couldn't take much, but I would have thought a standard timber floor with joists and bearers at the correct distances could take it. However, timbers do get a bit loose at times. If you're at all handy, you cna strengthen them yourself and deal with the squeaks and possible loose spots by getting under the house and putting in small wedges, or even checking the bearers to make sure they're in good order. Sometimes a new floor will develop new squeaks because it wasn't fully seasoned to begin with. We get squeaks etc in Australia, because we get either heavy rain, or months of dry weather. The floorboards either swell in the damp, or dry out and shrink. Very annoying.
If you opt for the "let's check it out" route, try to involve the boys to turn them into potential handemen. Even if all they do is find the squeaky spot and stand there, while you crawl underneath.
On the dyslexia front, have you investigated coloured glasses? I'm not sure what the view is these days but it was big in Australia back in the 70s. I think my optometrist still uses this, so I figure it's still believed to help. It needn't cost a fortune, so be wary of people who want to charge you an arm and a leg.
I hope this helps.
Marg