G.F.
My boys are 2 years apart and we had the same transition. Be firm and loving with the older one and DO NOT allow him to whine. This is a habit that he will rely on for years to come! When my son would have a fit, I would calmly put him in his room and tell him that he may come out when he's quiet and happy. (this was not easy and there was first more screaming.) I would make a huge deal out of it when he quieted down and praised him a bunch.
He's part of a larger family now that does not revolve around him and he needs to learn to love his sister and be cooperative - something toddlers just are not good at. I tried to make sure there was something to occupy his time when it was time for nursing. After nursing, the baby would be awake for a bit and I'd read to my older son with the baby together. When sitting down to play, I'd have the baby there too and made it a "kid" time instead of so much one-on-one. When the baby went down for naps, then it was one-on-one with him and I'd incorporate chores with him, "help mommy put this in the wash machine/dryer...can you put your plate on the table for dinner?...can you pick up 3 toys for mommy so we can vacuum?...can you throw the diaper in the trash for mommy?...Oh! Thank you! You're such a big boy!!" This also trains your kids that it's not just mommy's job to clean the house - everyone is responsible.
It's hard to watch their transitions but it's best for him to learn from the start that things don't go our way all the time and we can't just whine about it. We followed "Baby Wise" loosely to get the babies on a schedule from the minute they were born. The learned how to sleep through the night within 2 months. Maybe you can't spoil a baby but you can teach her poor sleeping habits by not setting the schedule for her. Every 3-4 hours of Eat, wake time, sleep, eat, wake time, sleep. Doesn't have to be rigid or rule your life but that cycle will serve you all very well.
And don't forget that transitioning to 2 is a very hard thing. You're still recovering physically and hormonally (!!) and low on sleep. Cut yourself some slack, girl! This is hard stuff and you're doing a great job! Keep loving on those babies! You'll all fall into a rhythm soon. Hang in there!
:o) G.
SAHM of 2 beautiful boys, 6&4