Hi M.,
According to my experience (I do have sole custody of my 3 young children and their father only has supervised visitation) - this is my advice...
Next time you go to court, ask the judge/magistrate to assign a Guardian Ad Litem (GAL) for your children. A GAL is the children's attorney (not yours - not your ex's, the GAL's only focus is to speak on behalf of the children). The judges know who the best GALs are and they will think "highly" of you for asking for a Guardian Ad Litem rather than them having to assign one to the children anyway... Also, based on your income/his income - the court will pay the GAL fees and/or your portion of the GAL fees and your ex would probably have to pay his portion!
Look into legal representation for yourself by interviewing other attorneys... This way you can say (to a judge/magistrate/GAL) you have been looking into finding an attorney (some attorneys may take on your case Pro-Bono or handle your case for a minimum flat fee) - Similar to the GAL, you can ask a judge/magistrate to assign an attorney (even one you've interviewed but can't afford) Pro-Bono based on your income/circumstances. If you find an attorney you like/respect, after interviewing them see if he/she would consider taking on your case Pro-Bono and/or what their flat fee for representing you will be?
The new wife... Think of it this way, your ex never had a problem choosing a good woman, right? After all, he had you (for a while anyway)! Your goal is and always should be to have a "healthy" parenting relationship with them. (In the end, a healthy one could mean minimum visitation)... So, include her in on everything, ask her for her opinion, let her show her true colors (to you, to your ex, to the GAL, a judge, etc.) It could be that if he does receive any custody - you might have some comfort knowing she's there too! She's probably a "good" person especially if she's been encouraging him to have a relationship with his children. And from what you wrote, you did agree to him having some kind of relationship with his children back in August. Joint custody isn't so bad as long as you are the sole residential parent (it is shared parenting you don't want)!
I hope this helps... I will keep you and your children in my prayers! K.