Picnicbunny I think you are in a totally shit situation made much worse by your spineless husband and your meddling cousins and mum. 
Thisthingcalledlife has written an excellent post and in your shoes I would take her words to heart.
If I am offer my own perspective as a Christian, a feminist and a woman.
IMHO forgiveness is primarily for the benefit of the aggrieved person (you in this case), it is a way of cutting off the past and saying that you will not allow it to control you anymore. If you are truly at this point, you can forgive your brother.
If so, you can do this in your heart, in your head, you can tell him, write him or simply never mention it.
It is for you, and if you have any religious beliefs then it would also be 'for God'.
As a feminist I am continually appalled at the evil done to women by male members of their own families and sometimes sanctioned by other females, it is revolting.
As one woman to another I would say do what you, in your own heart, wish to do. Do it and say to yourself whatever the future holds you will stick by your choice to go or not to go.
Seriously, what loss is it to you of the man who beat you unconscious? He made a choice to do that as an adult to a child. If he lives or if he dies, seriously, what importance is it to you? Now to explain that to others would be hard, and painful, why should you have to explain this.
If I were you, I would be seriously very upset by the actions of this weak husband. Any future discussion of this would be on my own terms.
I would also be furious with mum and cousins. It is none of their business what you choose to do. I have no idea how many of these family members know your history. Whether you choose to tell them or not is your choice.
IMHO you need to develop a broken record "I will not be visiting my brother." Or "I may visit my brother but I will not be discussing it with you." Do not be afraid to put the phone down on them.
In a short while you may be faced with whether or not to attend a funeral. Again do as you wish. You have one life. This evil man nearly took your life from you, the fact he failed is not done to his wise judgment but just down to luck.
To be honest Fuck Karma, you are responsible to yourself, be true to yourself.