Text messages are really difficult to use as exhibits in court — screen shots of long, drawn out texts aren’t effective as evidence at all, but sometimes they’re the only things available. This app exports and prints iPhone texts, messages, and photos, for documentation. [I have no financial interest in this app — wish I did.]
My first advice is still to use email, and preferably a dedicated parenting email program like Our Family Wizard. My second advice is save, organize, and print your important parenting texts using this app or something like it.