How do I keep a non parent from becoming involved in a custody battle between my first wife and I?

It what you say is true, then you had best get the an aggressive family law attorney. Not having an attorney is a big mistake in a custody dispute. There are preferences for "joint custody" which may not be best in your case. As such, you need to prepare to vigorously assert your custody claims and concerns to do what truly is in the child's best interests.   You need to get with an aggressive family law attorney who has experience with divorce, custody and difficult cases. I know what these cases are like, having handled a number. And you'll need my help in both cases, if nothing else then an attempt to shut the current wife down from causing your problems in the other matter.  You need to get moving ... as in today, to hire an attorney and handle this matter correctly from the outset. Or, you can try doing it yourself, and bumble through. Of the two options, which choice is best for your children, and your rights with those children? You should be able to get in with attorneys in the next day or two, I know that I have some openings.