Drop the nap and move bedtime up 30min of an hour

The bedtime pass may be your best bet.

https://www.npr.org/sections/health-shots/2015/09/18/441492810/the-bedtime-pass-helps-parents-and-kids-skip-the-sleep-struggles

At 3 I would go with outright bribery. If he stays in his room until 7am ( or whatever works) he gets X. I would include all the kids though so the older one specifically doesn’t feel like the 3yo is getting a reward for something he does without getting a reward.

Our 3.5 year old was previously a great sleeper. We moved in September and that threw everyone for a loop. He started refusing to nap so our nanny would lay on the bed with him and then that turned into us doing that at night (slippery slope). Now we have to lay with him to fall asleep at night and he comes into our room at 4 am asking us to come lay with him again (which we have been doing so everyone else can sleep). How to we fix all this? He shares a room with his brother (6) and his 18 month old sister sleeps next door.