D.D.
Two is just a tough age. They are still babies who need mama but have some control over things in their world which can lead to a lot of frustration. Add that to you being tired by the additional responsibility of a newborn who doesn't sleep all night and a toddler who is up all day. It's exhausting.
I always had a rule that the toddlers were never allowed to touch the baby. They could be helpful in other ways but touching was off limits. It just made it easier since it's hard for a toddler to be gentle.
Two yr olds also have poor inpulse control and they tend not to remember things for very long so you'll have to remember to tell your little one over and over that people do not hit other people. You can say something like: I'm going to hit you! No, people don't hit people but I can give you a hug. And then you give the toddler a hug.Then when your 2 yr old comes over to hit say oh no people don't hit people but maybe you can give a hug instead.
As everyone has said you or your hubby needs to spend some quality time with your toddler. When you are not busy with the baby take 10-15 minutes to play with your 2 yr old. They love to feel included so I always let my kids pick out which outfit the baby should wear, which socks the baby needed, which diaper was to be put on next.