Your husband will not be allowed to come to the house because he assaulted your son. I don't know if both assaults occurred at the same time, but police take assaults against children very seriously (as they do with wives). Until police and social services in partnership have investigated and are satisfied that your husband is not a threat to your child he will not be allowed near your son.
Ultimately the childs safety is paramount. If your husband returns to the family home before the investigations have been completed, the agencies may chose to remove your son.
It can take some time to investigate such complaints, but they will try and be as fast as they can because they do not like to disrupt the family life of children.
Perhaps if your husband speaks with police/social services about why he has attacked his brother and hit his son they may be able to offer him some assistance, such as anger management or parenting classes.
I hope this is some help.