It's how kittens learn what is exceptable or not and the squealing is the lesson. In Nature the mum cat, teach by a squeal if it hurt , a paw tap on nose if very bad, and also will ignore thir attention. The litle learn that it is not good to do what ever they did. The best way to teach good behaviour to a kitten is another or mum
So i would def leave them to it and they will learn what the others limitations are.
With my two and all of my lads i have had, ignoring is the main lesson where they just walk off if the other is getting too rough. Lol Garfy is the little terror and he litle to play rough. Marl is the one to mainly submit even though he is bigger and more muscular than Garf. Garf has a stronger personality and is a cheeky little imp! Marl is the softie but he def has learnt to give Garf as good as he gets!!
The "roughest" cat we have had has got to be Gizzy, we reckon he was a feral kitten and he was the only one to tend to bite and scratch your hands from kitten and in adult age. We had him from 7 weeks old (found in the near woodland) and he never learnt off Rio who was the softie. He hated his back touched at times and would tell you off!! I was worried that Gizzy at 2 years old would be too rough with little 10 week old Garfy but Garf loves to play rough and they got on great
Their play was very rough but Garf loved it and alsways started it!! Gizzy taught him when enough was enough!