Child custody cases are serious matters that can bring out the worst in the parents because each adult has their own idea of what needs to happen. There is no guarantee that those ideas will be the same; however, both adults must work together to make choices for the children until they are old enough to make them on their own. We know that this isn't always easy, but putting the kids first might help.
When you put the children first, you are putting your own wishes aside and doing what needs to be done for them. If your ex does the same thing, there is a good chance that you will be able to provide your children with an environment that enables them to thrive.
You might not always find it easy to work with your ex in these matters, but you have to be willing to pick your battles and to exercise patience. You can't always fight for what you want in every case. If the kids are happy, healthy and safe, you can likely leave well enough alone.
It might also help you if you remember that your ex also loves the kids. Just because the marriage didn't work doesn't mean that they aren't a good parent. In fact, you are likely not even seeing how good of a parent they are now since you aren't there to monitor their interactions with the kids.
You can include terms for making decisions about the children in the parenting plan. Make sure that this is clear so that there isn't any room for guessing how conflicts should be handled.