There are a couple of things happen at 2yo - one is that many LOs go through some sleep disturbance over their birthday period (and half birthdays too) so it is a common time for being confused over sleep needs and sleep disturbance. The other is that some LOs drop the nap at 24 months whilst others keep on with the nap until they are 3yo+. Either of these things, or both, can be effecting your DS's sleep.
It's very common for LOs to need help with the 2-1 nap drop so I wouldn't read much into that - it doesn't mean he has trouble with sleep it's just a tricky phase, I had to help mine every 20 mins during the drop to one nap even though he had previously done a predictable 2hr nap no problems for a long time.
You also said his sleep has always been difficult, so perhaps it is just his nature to like a long time laying quietly thinking about his day at BT before drifting off - if he is laying quietly then I wouldn't worry about it. The reluctance to nap I would focus on more and see if you can get that more consistent.
Do you see any links in the activity prior to naps times when he will fall to sleep more easily or has more difficulty? For instance a link between having had more social interaction at a mum and toddler group leading to it being harder/easier to nap or perhaps more physical activity leading to it being harder/easier to nap? This can be key for some LOs this age.
I would continue to keep records of your EAS times but also jot down what you did each day - if you have regular groups you attend etc and see if a pattern develops.
I would make nap time a very predictable time, set it at the same time every day regardless of what time he woke in the morning. So, lets say you pick 12.45pm and stick there. Then do not let him sleep beyond a 2hr period, so regardless of what time he fell asleep for the nap I would get him up by 2.45pm even if that means he only fell asleep at 2pm he gets up at 2.45pm.
I would maintain bed at 8.15 if that seems to be working relatively well, laying awake is fine if he is not fussing or complaining and it looks like his night length is reasonably good.
If you can bring this level of consistency into his nap (the put down time and get up time) he still has flexibility to take more sleep if he needs it or less sleep if he doesn't, he can regulate his sleep needs within the predictability of the routine. It could take a couple of weeks or more to settle into it - and as I said around 24months sleep can go off track anyway so it can take longer to see the long term results due to the developmental phase.
What do you think?