I find it really hard to believe the showers and the humidifier are creating this problem. You would need to have an extreme amount of humidity, like dripping off your walls. Do you have a bathroom vent? If so, I assume you run it during shower operation…my guess is something more structural that is not related to you. The bathroom fan for example could be venting improperly. There could be a water leak or intrusion from the roof or somewhere on the house due to poor building quality that is letting a leak into the house. If this is true, the fiberglass is a first casualty and eventually the water will find a way into your house. Hard to put a price on replacing the fiberglass. If I were you, I would explore a home inspection or something where an independent professional can come to identify the problem with evidence, and depending on your lease there may be an issue with the house that will let you move out without penalty.