The OLDER kid, should be punished.
Simple.
The age disparity, between a 4 year old and a 2 year old... is a lot, and developmentally.
Your 4 year old... is ON PURPOSE, doing this, to his younger brother.
On purpose.
He is trying... to get his younger brother, in trouble. That is also, obvious.
You need to SIT him down.... and you AND Hubby, talk to him, concretely... and call him on his behavior.
I would.... TELL him, that you KNOW he is doing this on purpose, that you SAW him do it, that you are not dumb... and he CANNOT FOOL YOU.
You need to tell him, you are onto him.....
Or film him doing it. Then show him.
If you don't correct this now... then what? He will get older and worse.
He has to have, FINITE consequences.... and, you AND Hubby, sit him down and tell him, BLUNTLY... that you are onto him... that he cannot fool you and you know he is causing, trouble, on purpose.
AND that... it is MEAN. Mean to his brother, to you, to the whole family... because... a family does not 'harm' each other nor get each other in trouble. A 'family' should have each other's back... and watch out for each other and HELP.
You TEACH him, what a "family" is... and he is a PART of that... or not.
Your son is 4. You need to tell him, in a grown up way, not talking to him like a baby... and tell him... that is simply NOT ACCEPTABLE.
AND you teach the 2 year old... NOT to follow his brother... but to TELL YOU.... when brother is causing trouble and causing harm.... but also tell your 2 year old... that he cannot act that way.
Again, your 2 year old... is being 'taken by the hand'... by your 4 year old... and TOLD what to do.
Younger siblings... often, do what their older siblings say.
I know, I am the youngest sibling.... among real bossy overbearing obnoxious siblings. One of them, 'loved' to see me get punished... just loved it... in real cold mean way. That sibling, was always, 'jealous' of me. For whatever reason.
You teach the 2 year old, HOW to stand-up... to his older brother...
all the best,
Susan