IME part of the challenge at this age is that their little brains are wired 'literally' and when processing information they often do not 'hear' the negatively phrased directions just the 'direction' .... so when we say 'no jumping on the couch or no hitting' and so forth all they hear is 'jumping on the couch' or 'hitting'.
My advice would be to try instead focusing on what you want him to do ... wording it simple .... feet stay on the floor, hands to yourself, toys go in the bucket or whatever it is he 'should' be doing that he is not doing ~ see if that helps.
I also agree that children often react to 'newbies' in the daycare either your own new babe or a new daycare babe just like a 'sibling' would ~ so definitely looking for tips online about dealing with sibling rivalry and how to flip the child to feeling 'good' about the new addition ... I have success with assigning them 'big helper' tasks that make them feel important as well as making sure that I still set aside some snuggle times.