It's normal....its all about "ages and stages."
Read up on each age group, and it's characteristics. Arm yourself with understanding each age. This helps a great deal. No matter what, some things just won't work, unless it is taking into consideration what stage and age the child is. Sometimes, "discipline" methods will just go over their heads.
A good book is "Your 4 Year Old" or "Your 5 Year Old" You can get it on amazon.com
At 4 yrs., they are changing a great deal.
Like anything else, if you want to be successful at something.. what do you do? You learn about it and research it right? Or learn about your "opponent" (as in sports) and then reflect on that and see how you can get better at understanding them and do better, right? Well, the same for a child that we have... we must FIRST learn about them...not use generic things on them, and then once we understand THEM... see what we can do to improve them or us. Yes, Parents too, have to learn and improve, in relation to "how" we handle our children in the best way possible.
Some phases, you just have to ride it out... and it's irritating....but pick your battles and choose how you interact with him too. Kids spend ALL day and everyday... being at the short end of the stick, and being told how they are NOT being what we want. How fun is that?
Another important thing is this: He is your ELDEST child, and he has a younger siblings. Ya know, for a 4 year old...to be 'EXPECTED" to be 'perfect' all the time is just NOT feasible. They are not mature enough mentally or emotionally to "BE" everything to everyone, at all times. It's a hard thing to be for a young child... and, it's a "role" they simply don't want at times. We have to be cognizant of this. They are, by "default", the child that has to put-up with everything, be perfect, be obedient, be good, listen all the time, do everything, AND be a scape-goat for their baby sibling. This is a LOT of pressure on them.... they can't be expected to KNOW automatically how to cope. They need help themselves, in how to cope with it all. It's a big burden to have on their shoulders, day in and day out. It cannot be. It is often said, that eldest siblings sometimes don't have a "childhood" of their own... because they were always expected to ACT "older" than they were, and more responsible than they were, and to just be everything and help and perform and listen and be "good" and "please" everyone, all the time. Meanwhile... they didn't even have a chance to be nurtured themselves or be asked "how are you about having a sibling?" They have no choice in "choosing" to be an eldest child... and with any child, their moods fluctuate. We have to allow for this.
He probably does not like big crowds because it is stressful for him, and then there are MORE expectations upon him. Egad!
Run for the hills!
Do NOT put all the pressure of "having a peaceful family" on his shoulders. It's not his responsibility. Certainly not at only 4 years old. Yes, you want him to be happy...but he is obviously not... and is not getting what he needs, internally. The poor guy probably also feels marginalized by everything, and it is not only the Mom who had a baby...it is him too. HE had a baby too! His sibling. But, all he is told is scolded or told "no" or have exasperation and frustration looking at him in the eye. How disappointing for a child.... they can never "live up" to what the Parents want.
I have a 2 year old, and my daughter is 6 (but was 4 when we had my youngest child). I made EXTRA sure that I prepped her for having a sibling and they adore each other. But she too, goes through spurts of simply NOT listening to ANYTHING I say... and she will tell me point blank- "YOU LOVE BROTHER MORE THEN ME!" Yelling that to me. It hurts... the child. But instead of "correcting" her... I hug her, spend time with her, I actually apologize to her that I make her feel this way... and we "make-up." In our hurried lives, we often forget what the other oldest child truly needs. My daughter will even, when I am busy... tell me "Mommy... you didn't hear a thing I said, I tried to be patient and ask nicely... but now I am MAD! You need to apologize!" And, you know what, I gotta love my daughter's articulate way of expressing herself...and she IS right. I admit it. Sometimes I get SO busy, everyday, and since she is the oldest, I "assume" she's fine... but they are not. They feel "neglected." Kids NEED a LOT of us, and from us. And we HAVE TO listen to them in their hour of needs.
Kids, will most often be this way when they are not getting what they need. At least for my daughter that is the case.
Their internal and emotional well-being is what is important. If not, well, they won't respect us, or listen. If we don't listen to them, why should they listen to us?
All the best, sorry for rambling,