NoryCaw said:
Any input would be helpful, I just don't even know how to process this.
Under the circumstances it would be quite reasonable for you to disown your entire family. You should also consider becoming an Atheist.
Seeing your first child seems to be impossible. Trying to do so will put you in a toxic situation that will damage your heath with anxiety and possibly lead to violent conflict. Even if you do nothing to initiate this there won't be any unbiased witnesses and you will get misrepresented.
It seems as if you now have a second child, I hope by someone who you have a good relationship. She must have parents that you can have a healthy relationship with. With any luck they live some distance away, perhaps out of state. If that is the case move closer and spend more time with them as a result. Don't see your first child at all. Yeah, I know... that is really tough advice, but a clean break will be better for you both.
Don't forget about your first child though. Pay ample child support and send gifts on their birthday (NOTE: they may not get them...). There is an outside chance that your first child will rebel against its mother when it becomes a teenager and want to know about its father and come to see you. Even if the mother prohibits this, there will be no stopping it when it becomes a financially independent adult. It may secretly visit you when it is thought to be at University. I know that this is a long time for you to have to wait, but if you can understand that they may feel like blaming you for your absence (having been told a bunch of lies their entire life) and don't get indignant with them for their behaviour and just spend time together as a family with their half-sibling and not spend the entire visit stuck in the house, you may be pleasantly surprised at the positive change in their opinion of you. With any luck you will have your second child saying that you are a nice person.
However, avoid any "my first wife was evil" stuff around your new family as much as you can. As your second child won't know for sure if your version of events is the truth and your first child may well suspect that you have "brainwashed" your second child to say bad things about their 'evil' mother. Just neutralise the toxicity. Seek therapy if necessary.
Honestly, if I knew of a way to get you all back together without this woman I would suggest it.