2 year old suddenly doesn't sleep? Please help.

My son is 2 years and 2 months old, always been a great sleeper (besides newborn age), usually just put him to bed around 7 and he will play around for a little bit and fall asleep, wake up about 6 or 7 in the morning. Also would nap roughly 1-3pm.

Now this month has been really difficult, he hated the NYE fireworks he could hear from his room, he had his first sleepover at his dad's house (recent seperation, only stayed there once so far), he started nursery 2 mornings a week, he spent a night in A&E, we've had some really stormy weather and he gets upset at sound of the wind through his windows, and he's had a croup. So a lot of stuff going on in a short space of time.

Now I put him to bed at 7, mostly he still goes to sleep like normal, although sometimes he will still be awake at 9pm trying to play. But he wakes up during night crying hysterically banging at his door for me to come and get him. If I settle him back in bed and leave he instantly starts getting out and crying hysterically again. If I stay with him he thinks it's play time and won't sleep. He's also resisting sleeping at nap times and sometimes only sleeps for an hour.

Now I really need him to sleep a bit better, I have a 6 month old also and he keeps waking her up and between the two of them some nights I only get an hour's sleep. Do I drop his nap? Or do I just keep persevering with his regular routine in the hope it's just a phase? Or any other suggestions? He also has developmental delays, so I'm not sure if that's related and he doesn't talk so he can't tell me what's wrong.