There is one important rule for growing tillandsias, especially indoors: after watering they must get dry fast (within 3-4 hours recommended). For that they need comfortable room temperature, some light and most importantly fresh air. Never close them inside glass orbs or mini greenhouses. If they stay there damp for too long, they will rot.

Watering frequency depends on conditons/weather. Misting them 2-3x per week is enough during winter. Fertilizer very diluted, once per month.

If your other plants look bad, there is very high chance that they are already infected by rot and will soon die too.