OK, I think he's just getting a bit overtired and overstimulated. At this age we would expect him to be able to handle about 1hr20mins MAX awake (including feeds) - and after a short nap, even less, maybe only 45-60 mins.
So the first thing is, re overstimulation, I know it must be so hard with a busy toddler around, but I am wondering if you could try having him in a sling for the first A of the day, so that he is close to you and therefore more relaxed. I would also start his wind-down earlier, so that you are getting him to sleep by about 8.15 (so starting to shush-pat around 8?). It might be that if he can get to sleep a bit earlier, he finds it easier to stay asleep.
Now, remember that if he still has a short nap, you will need to bring his next nap earlier. Don't keep it at 11am if he has woken up from his nap at 9am or he will be overtired for sure.
Finally I think bedtime needs to be earlier. If he wakes at 7am I would aim to have him in bed and asleep for the night by 7.30pm at the absolute latest. If he is awake for the day at 6am, then bedtime is 6.30pm. If he has had short naps all day and been resisting sleep, then I would do an even earlier bedtime. Again you may well find that helps him to fall asleep easier without you having to spend hours with him.