My sister as far as I know hasnt talked with the local police as of yet. In the past while they were still married he threatened to kill her before and I took her to the local police and they didn't do anything because there were no physical marks, even though she had the threats on her phone cause he threatens her via texting and the police didn't even look at her phone. So that is why I am trying to gather as much information for her to go about gettin full custody of their children as well as some kind of protective order against him,
Sometimes people have a tendency to brush off threats to kill as "just talk." In abusive relationships however, threats to kill are a considered an very serious risk factor that indicates the women may be 15 times more likely to become a homicide victim than abused women who have not been threatened in this manner. In the world of domestic violence, threats to kill are very serious.
Whether or not his threats to kill are sufficient to get a restraining order however, is going to depend greatly on the local legal climate. Some courts operate with an abundance of caution and hand out restraining orders under a better safe than sorry mode while others require much higher levels of proof. Your sister could speak with her local domestic violence outreach program (free) to find out more about the local court climate and whether a restraining order might be possible and helpful in her situation.
If she decides that a restraining order might improve her personal safety, an advocate might accompany her to court and help her file for the order. She can visit http://www.aardvarc.org/dv/states/menu.shtml to find her nearest local resource. The state and national domestic violence hotline will be happy to speak with you as well.
Your sister is ultimately going to have to choose the course of action
SHE believes is best for her, but you can certainly be educated on the subject to be in the best position to help
IF she wants help.
and for him to only have supervised visits with the kids because this week he is now telling them stuff and messing with their heads.. the whole situation is yucky to be nice about it.
The restraining order may be a possibility for your sister, but based on what you have described, the likelihood of her ex getting supervised visits is between null and non-existent. Even in cases where there is documented proof of physical abuse toward a spouse, there is often unsupervised visitation for the perpetrator of that abuse with his(her) children. There would be a substantial burden of proof for your sister to prove that her ex is a danger to the children and get supervised visitation. Beyond that, emotional abuse by messing with their heads is not illegal even if it is very damaging from the psychology standpoint. The ex messing with the kids head is not going to be sufficient to get supervised visitation.
Domestic abuse victims often need significant help exiting abusive relationships. As her sister, you can be valuable support. Part of that support, hopefully, will be helping her trust herself and her own decision making. There are lots of books for people in abusive relationships or leaving those relationships. There are not a lot of books of guides on how to be the helper of someone in an abusive relationship. Susan Brewster has written one of the few books on the subject of how to support someone in an abusive relationship. You might find her stuff worth reading.
Good luck.