@Love I really like your response here. Give people the benefit of the doubt until proven otherwise. This woman is her ex husband's wife now. I think it will be very difficult to avoid her over the coming years. It really is best to try and make peace if at all possible.
@mairej You want to appear like the reasonable one to the courts. Don't do anything that infringes upon your ex husband's parenting time. Don't call him or her names to others. Don't badmouth dad in front of the kids. Even if you feel like she is 'evil' don't go around telling people that. The court doesn't care about your opinion of your ex husband's new wife. The court is not interested in your different parenting styles. They only care about what is in the child's best interest. And sadly that best interest standard is a little subjective. But one thing many courts have started to recognize is conflict is bad for kids. If you come across as uncooperative and unwilling to work with your ex for the sake of your kids you look like the bad guy. If you withhold your kids from your husband for any reason other than provable safety concerns you look like the bad guy. And for goodness sake absolutely don't lie and make up false claims of abuse against them. The courts in my state take that so seriously you could lose your kids over a false abuse claim.
With that said...I have no doubt things are hard right now. I'm sorry you have to go through this. It's not the dream we all want when we think of raising kids. You might want to start documenting especially if you've got the threat and conflict of court coming your way. You can write a couple of sentences with a date every time you have an encounter with your ex and his new wife. If nothing happened just state that in a journal. You can also purchase a little USB recording device. They usually hold around 6 hours of audio. It's discreet and it picks up conversation even in your purse. Amazon sells them for around $25. Make sure it is legal to record in your state without the other parties knowledge before doing that. Absolutely take the high ground and try to be the more reasonable parent at all times. Be respectful in person and in writing. Only address matters pertaining to the children and keep it as brief and friendly as you can muster. Practice if you must before engaging them and stick to a script. That is the long game. If they are crazy-making you will eventually get that caught in your journal or in a recording.
If you are concerned about domestic violence and you have actual evidence that something occurred to put your child in danger than that is a very serious matter. You need to engage an attorney right away and/or the police. If you are simply concerned about the possibility of domestic violence that is a something else. The courts are overburdened and not particularly interested in hearing an opinion based on someone's colorful past. They would be full of angry parents singing the sins of an ex nonstop if that were the case. If you think your ex husband was fooled into marrying this woman and you've got her number but he doesn't... don't worry, these things have a way of eventually coming out. Be patient. You can not be the one that enlightens him. You might start having your child attend sessions with a child therapist. If anything untoward is going on you will have a neutral party who can speak to that. The courts will see you as biased so it is best to get a professional.'s opinion.
Good luck and all the best!