Unbelievable weak parenting here. Its a kid. Kids need rules. You let him away with something like this once and you deserve all the unrest it brings. Just you wait, the 8yr old will spot the weakness in your parenting and start copying it or decide there must be something else they can do to wind up daddy.
Someone suggested taking something away. You then say you have taken away 4 of his dummys for gods sake. That in itself suggests he lost his 1st dummy but had 3 back ups. Wow he must have been gutted.
It is in a families interests for the kids to know clear boundaries. Bedtime is one of that is black and white. If they go to bed, they go to bed to sleep and only leave the room to go to the toilet. Other than toilet breaks both my kids, even at 7 & 12 ask if it is time to get up yet. Its not military and they are never told no. Its called respect.
Take the kid to one side, explain that bedtime is for sleeping and nothing else. Ensure he has 100% darkness in his room for bedtime with the use of blinds etc. He should not be able to play with his toys at bedtime but if he has a teddybear then my lad used to sit for a while playing with his inner sanctum of cuddly toys doing wwf wrestling. Always found him cuddled up with them asleep.
Now the big secret for a happy bedtime. I was told this by a midwife and it worked for both my kids from the age of 6wks old they have given full nights sleep.
Have a routine for bedtime. Every night must be the same. Play, calm down time, bath time, brush teeth, cuddle for 15mins then bed. Every night. Its like a signal to the kids body clock that he needs to get into sleep mode.
If the little one wakes up at any time you should NEVER give him any more than the most basic attention. Never have a discussion with him and never let him win even if his tantrum takes all night. Even if it escalates to a dirty protest!!! If you give in just once you have rewarded his behaviour with the attention he craves. A child waking up in the middle of the night is usually just bored or needs the toilet.
All sounds a bit blunt but if you have a tired child and tired parents then you cant give him the full love through the day. A bit of authority through the night means you can be so much happier through the day.