T.N.
I HIGHLY recommend reading Parenting with Love and Logic or watch one of their DVDs or go to a class in your area. http://www.loveandlogic.com
See it from his point of view. Of course he doesn't want the day to end. That means he has to stop playing. And it's time he gets to spend with both of you, and it's hard to share you with a new sibling.
Now that you can empathize with him try to set some limits around bedtime and firmly enforce them with love instead of yelling. He's running the show at bedtime with all the runaround he's giving you guys. He knows that and it's a way to have control. He's testing his limits and pushing. Try to set up a simple routine and make it very clear to him so he knows what to expect. Explain that after A, B, C, then lights out and you're leaving the room. Obviously you can't force him to fall asleep on command, but leave the room (childproof the door from the inside if you have to so he can't get out. Pull the string on the light so he can't turn it on with the switch). Draw pictures of his routine or print them from the computer, maybe laminate them. To give him some control that you're okay with, let him decide the order that he gets to do the routine. He can pick the toothbrush picture or pajama picture first, or whatever he wants as long as he does all the pictures. He'll like to be able to feel like he's calling the shots and making his own decisions. We all like to feel independent and it's an important part of developing. Then when you're done with the whole routine (after my kids are ready for bed I read a book, talk a little about their day and say what we're grateful for, sing a song) lay him in his bed and lovingly leave the room and shut the door. Leave a sippy cup with him before you go so he won't beg for water. Of course he'll cry. It's worked in the past for him. It will be extremely difficult, but BE CONSISTENT and he will learn that when the routine is over, he's in his room for the rest of the night. It will carry over and he'll respect you in other areas as well. He'll obey better when he knows that you enforce the limits you set. And your relationship won't suffer because even though at first he'll be sad, you will no longer be ending the night in tears and anger. Soon the bedtime routine will be looked forward to by all of you as a time to bond and cuddle.