If you had a teenager (X) who was rude to a sibling and hit them, it would be considered normal (Although immature).
If X was now in their 30s and still behaving this way, can it be brushed under the carpet as just immaturity/normal sibling behaviour or does it become emotional abuse?
X still acts like a teenager in many ways. I am not sure if there is still any physical violence as this hasn’t been shared with me (although I wouldn’t put it past him).
Some of their behaviour includes calling their sibling very derogatory names, shouting a lot, being very controlling with sibling and putting them down/ making them seem untrustworthy infront of others. I have witnessed this in the past and am ashamed to say I believed what X said about their sibling (he’s very convincing) 
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I have been deliberately vague about details as I am posting for someone close to me with their permission and don’t want to write anything outing. Deliberately no mention of why siblings are living together etc so please don’t just say they should move out etc as it’s not possible at the moment.
I personally feel X’s behaviour is emotionally abusive but it seems to be falling on deaf ears. I think unless it’s said by others too, it won’t be believed.
And if others do feel that it is, is there anywhere that can offer help or advice? Most places are for partner to partner abuse and siblings not considered or covered.
I have tried to cover everything so as not to be accused of drip feeding. I can try and answer any questions but may not be able to of it might be outing, so apologies in advance for that.