I have twins here also and they've actually gotten very good at analyzing each others mechanics whether it be pitching, catching, batting, etc.
If my twins started analyzing each other I imagine it would always end in an argument, no matter who is correct.
Any general advice for another father of twins? I have a very difficult time getting them to practice at the same time. Ironically, one is a catcher, and one is a pitcher. They know how good it would be to practice together, but that won't stop them from arguing. The pitch won't even let her sister catch for her during her pitching lesson.