T.S.
S.,
My older son (a Mama's Boy at the time) was 26 months when his brother was born. Of course, we prepared him for it. Told him "Ryan" was coming home. Let him help in Ryan's room. Showed him where the hospital was, etc. But really, we just made it part of life and not that big of a deal. He "helped" us by getting diapers for Ryan when it was time to change him. He sat by me when I nursed or when Dad fed Ryan and we made a point to let Jacob (older son) have some one-on-one with Mom and Dad at different times.
I really think the behavior issues are just normal, challenging 2.5 y/o things. You are absolutely doing everything that I would do. Ignore the tantrums. Explain the consequences, "If you hit, you will go in time-out". Praising the positive (big in our house). Just be consistent and he'll get it.
Hang in there. Pretty soon, you'll be able to watch them play together and your son will teach his sister things and it's just the best thing in the world to see!
Congrats on #2.