Hausabend is a chance for each Haus to take their food and have time together with just the people in their house and do something fun. Common activities are sports, watching a movie, going for a hike/swim/bike ride. This is often combined with a picnic or Pizza Lieferung.
Use this as a chance to bond with your house. Make sure you have something planned in advance and that you don't see this as an evening off. The kids really enjoy this time and you can make a very memorable positive experience for each one of them.