As well as the above - if this boy is 4.5 years old and is speaking very few words he needs to be seen by a Speech and Language Therapist. By that age you would be expecting sentences. There are many speech disorders and developmental disorders that have difficulties with speech as part of them. It is very possible that his aversion to school and his behaviour is down to simply not understanding language and what is expected of him. If his expressive speech (how he talks), or his receptive speech (what he understands is being said to him) are affected it will have a bit impact in school because most of the day involves listening to verbal information and having to communicate with teachers and children using speech. And he has also recently moved to another country and school as well. If he has these types of difficulties it is extremely 'normal' for him to be reacting with anger and frustration. Imagine how you would feel in an environment where you didn't understand the language and couldn't express yourself either and you had to stay there all day - day after day. How long would it be before you started to show bad behaviour?
So I would recommend his speech and understanding of speech as well as his social interaction, auditory memory and working memory skills are assessed. If that all comes back okay, great. If not you have identified his difficulties at an early age when any therapy has a much more beneficial effect.
Does this child have any sensory issues. Do they appear deaf when you call their name, or do they cover their ears at sudden unpredictable noise. Is their sense of smell, taste, touch over sensitive. Is their balance and co-ordination the same as their peers. Do they play with children the same age.
Do thry have what we here call bullying at scool where your Brother lives? do the other children pick on him, has your brother asked his son are there problems at the school, why does he not want to go, you say he is beating up other children, ,I would tell your brother to speak to the teachers and find out why this is happening there. Is he good and happy at home ?