When the older DD is stubborn about not doing something, sometimes her younger brother will step in and do it for her, to avoid her getting a punishment. I think his motivation is trying to keep the peace, plus he is a very empathetic person... Unfortunately, this doesn't happen when DS gets in trouble.

My 3 are like this too and I sort of love it (even though it’s frustrating in the moment). The fight v play well ratio is about 50/50 (they are 5/3/1), but if one of them is in trouble with us for reasons unrelated to fighting with the other two? They are in lockstep against us. My 5 year old also told off another 5 year old who pushed in front of the 3 year old on some playground equipmentand explained that you never do that to a younger kid and especially not to her brother, so he was going to have to let my 3 year old go twice in a row now. And then he did. It made the gang ups worth it

OMG it totally warms my heart when my kids band together and protect each other. I want them to have that kind of relationship with each other. That's the way it should be.

The 4yo's reaction does seem a little over the top - but you know, he's 4!

I’m 48 and my brother is 45 and my mom tells a story about how she yelled at me when I was around 4 because I destroyed my bedroom after she had cleaned and my little brother gave her an earful (mostly unintelligible) for getting onto me.

To this day, I have kept every secret I know about my brother and while we may fight like cats and dogs, if anyone did the same to him, they’d have to deal with me.

Oh! You are doing something right, op! Your kids love each other. My kids were like that, but around 7 ds exhibited insane anxiety and started hating his sister as she was "embarrassing" him. I was like this with my sister, still am. It is a wonderful thing to have.