Trail shoes tend to have much more pronounced grips on the bottom, which also tend to be of softer material than the outsoles of road shoes, so I think you'd find that they would wear out very quickly on tarmac. Also, as trails tend to be softer than roads and your feet naturally move more on an uneven surface, trail shoes generally have less cushioning and support.
In short - probably best not to use trail shoes for road running, other than a short distance to a trail....... certainly 2 hour runs would be problematic.
I have a pair of Adidas Response Trail shoes that I bought in my local running shop in the sale for £35. I only wear them for parkrun (ours is on grass, and it can get very muddy) and for the occasional off road training run. I keep my road shoes for road.
Gosh you have been busy! I'm 2/3 of the way through the 5x50 challenge - going great guns (including a parkrun PB) until I gave blood last Wednesday. Really knocks the wind out of your sails, but all in a good cause.
Has your boy tried parkrun? 10 finishes and he gets a t-shirt? No pressure to be first, but all your times are recorded so he can track his progress against himself over time? And against others in his age group. Even better if there's a junior parkrun in your area.
I think you know the answer Gabi - your times are declining for more effort and you are getting fatigue pain. Keep going and you will end up doing long term mischief. Overtraining is something to take seriously. I work with an ex-prefessional orienteerer who ended up not able to train AT ALL for 2 years due to serious overtraining. Ok, you are probably nowhere near her level, but a good rest now and a measured return to training could make the difference.
Simplifying, noise cancelling generates an inverse waveform for predominately periodic low frequency environmental noise, using little microphones and low latency active circuitry in the headphones. The tech first sprang up in pilot headsets, where that sort of noise is common, and being hear radio chatter is important.