From what you described I feel your 6 year old is absorbing both your stress and your husband's withdrawal behavior and it is not good for her development. Please work on keeping her doors unlocked always. She needs constant monitoring or at-least a parent checking on her every 45 - 60 mins and ask her how she is doing or if she needs help or support for school or otherwise. I would say after you build a workout routine and have control over stress immediately focus on your daughter's behavior and identify what parts of her behavior are her personality/nature and what areas are due to family environment or covid situation. Focus on the changeable areas and work on them. Coming to her personality on cleanliness and not sharing with brother, give her sometime and keep encouraging her in right direction.