Babies put everything in their mouths to explore and understand the world around them.  Most kids grow out of it as mobility and function develop.  The best way to stop a biting habit is to address it as soon as it starts.  Even a baby who bites at the breast can be redirected and told "no biting".  Most times gentle warnings work but if your child continues to bite then investigate if they are biting to get attention, are they limited or overwhelmed sensory-wise, or they may need help finding others productive ways to express themselves. 

That's a great question and there is no standard answer that is right for everyone.  Does your child have health issues or is there someone in the family that could be compromised by having your child around other children?  If the answer is yes then look further into how is your school district handling safety, masks, distancing and testing before deciding?  If you don't feel comfortable, find an alternative solution. 

How messy is messy? If we’re talking unhealthy with food wrapper or wet towels, intercede and set up the clear parameters with them for what’s allowed and what’s not. If it’s just regular messy, then you need to walk away and shut the door. We all need some private space and setting expectations for everyone in the family to clean the shared space is great but I think some creative mess is ok in their personal space.

First, take a breath!  Find your way to personal calmness and take a quick observation as to what’s causing and fanning the sibling warfare.  Do they need to be separated?  Is there an underlying unresolved issue? Is a ceasefire in order?  Bring them to the negotiation table and give them each 2 minutes to speak and then make them come up with two ways to improve their relationship. Set some ground rules, work out differences, and discuss expectations for household harmony and how everyone is going to work together to help them get there.