I'll be surprised if the other plants don't produce seeds as well. If it were me I'd keep hermie out and away in a sealed space, to help reduce the chances of having even more beans.
Pretty small for three weeks old. I'd increase my temperature to 80 to 85. Make sure to also have indirect airflow to help strengthen the seedlings. If you have a good smart phone down load a light meter app. Plenty of info here on light levels depending on the age of the plants. Good luck!