It's not immediately obvious, but you can get the partner(s) back to the way you want by clicking on "Change or delete" and then "Change partners". I had to mess with both partners to get this pack to showing them as married.
In answer to your second question, I don't think there is a way to have Family Echo arrange partnerships by date. It's a nice idea for a feature, and you can use the "give Feedback" button to suggest it.
