is it wrong?

Of course not. Why would it be wrong?

because maybe stepping over lines into being a parent is bad? im not sure just thought i would ask

Talk to your father.

And, BTW, it sounds like you could all use some counseling to deal with your grief. You should not be taking on these responsibilities at your age. It's not that you don't care; it's that it's not your job. It's your father's job.

if he doesnt step up though shouldnt i? i cant leave her to defend herself.

Defend from what? Is she being attacked?

I don't doubt that you are a loving brother, but you are biting off WAY more than you should have to chew.

Do you like it or do you fell crushed by the responsibility?

Jespah is right that it's your father's job. But then, you wouldn't be the first kid stepping in to substitute for some absent parents with his younger siblings...

precisely

You need to have a serious discussion with your dad.

If that discussion isn't working, then you need to discuss matters with a school counselor or counselor of your own. You mentioned about her having been abused? Where was he in this process?

Your dad needs to know your concerns and needs to understand that one or both of you need help with counseling..maybe himself too. This is his responsibility. Something isn't adding up here.

my father basically disowned my sister after the abuse because he was ashamed of it hapening to her.

He can't stick his head in the sand. There is no shame to her. His attitude about it is medieval and poisonous.

This is about her mental health..as well as your own- as well as his responsibility as a parent. Of course, he's dealing with his own grief but where has he been when the abuse happened? Was the abuser caught?

Where is his caring for her now? If he is dealing with guilt over the abuse...but then punishing her ... that is criminal. She's innocent and he's ignorant.

She needs counseling. If he ignores it, it'd be like tossing her to the wolves. He most likely need counseling, too. The responsibility is his. If he ignores it...it makes matters much worse. you can';t make up for his ignorance. No matter what, he has to be involved in her healing. you can help somewhat..but he's the responsible parent and adult..whether or not he takes the reins.

Can a relative or friend of the family ..some close relative or member of the church/temple..or community help bring this across to him?

I'll ask again...how old are you?

Not weird at all - very sweet actually and very normal. I think you might be questioning because of how you grew up. Usually families are looking out for each other - even siblings.

My two daughters are 4 years apart - they may fight like cats and dogs, but anyone else cause grief to one of them, they got each others back.

Normal, natural - and with your age differences and situation, I would imagine the protective feeling being even stronger. She is lucky to have a caring older brother.

Bring in another adult to help out. Is there an aunt or other older female friend that can help with this issue?

For sure, the best thing you can do is to get professional help for your sister.

How old are you two?

The OP is male/24. His sister is 13.