I know nothing, but am watching this post and answers closely since this will be me in a month! My ds1 is 4.5 and ds2 is 2.5 and I'm pretty sure ds2 has no freaking idea what is about to go on. He's all excited because ds1 is excited, and says BABY and touches my belly, but the kid has no concept of what that means for him and his amount of mummy time. Then again neither did ds1 when ds2 was born, and we got through it. Ds1 did a lot of poking and prodding ds2 when I wasn't looking (or when he thought I wasn't). I always gave him a time out, and explained why not. We still do that when they get too rough with eachother.
Agree your idea to give him attention when you can is good because that's what he's really saying, I want mum, and baby has her. Go easy on the lemonade or you'll get stuck with that as the official "reward time" thing (we've all been there). Swap it around, do something else he likes, weather it's a fave book, fave DVD, fave toy or puzzle or other semi healthy snack.
This is super easy for me to say because that's what I did with 2, however neither of my boys sleep in the daytime now, and I am yet to birth #3 so the fact you kept them all alive thus far is impressive to me, and I think you are doing a splendid job! Watch me crumble in 4 weeks time.

