Two things from the uncommon view of parenting (yes, I know, lots of people disagree with everything I say, I'm okay with that):
1. the time alone with your older lad is sending him a mixed message, one of intentionally exclusing the brother for his benefit, which makes his brother's presence look like a problem, and
2. telling children what not to do simply doesn't work, their minds can't hold the 'don't' only the rest of the instructions, so you're inadvertently following him around telling him to throw things. Btw, this is true of everyone else, too... it's almost impossible to 'don't' anything, but it is possible to 'do' all kinds of things: remember to do this, put things down gently, use words, touch your brother kindly, etc...
It will take everyone in your home some time to get to know this new human and his preferences and communication style, and the period of adjustment will only be really easy to the person whose temperament is the most like his. Everyone else will be shaking their heads, getting really frustrated or just being confused a lot of the time for another couple of months at least.
Oh, one other thing: if your older boy's experience of his little brother's presence is that now he can't do all kinds of things and there are all sorts of restrictions on what he can do, he's going to become more and more anxious over time which will further degrade his behaviour. Clear out your house (and lifestyle) so that it is okay for him to safely explore his world without a million 'no's every week.