Livestrong, the questions you are asking are perfectly normal and you are in the right place. However I want to caution that you may not like some of the answers you hear. That being said, the more knowledge you get, the better prepared you will be.
Now that you have reached this decision, you need to understand that by interjecting the legal process into your relationship, you may be presented with situations that are neither fair nor just.  :)o not get discouraged. When divorcing a BPD, in general the process can be painfully slow. One of the recommendations we make is to keep focused on the long term goal and keep the process moving.
I will also caution that you may not be able to achieve all of the goals you desire so it is important to be able to prioritize. For example, you stated
How does one remain living in the same home after just serving an over-reactive and very angry undiagnosed BPDH.
. The answer is that it might not be possible. You said you cannot leave because you have children in school. There a lot of factors in your housing but your prioritization might look something like this
1. Best scenario - you file for divorce and uBPDh and you are able to live in same house during divorce and you can feel safe. There are number of things you will need to do to protect yourself if this is the scenario, but more on that later.
2. Good scenario - you file for divorce and by his actions / reactions it is clear that uBPDh and you will be able to peacefully coexist in the same house. Now you have a decision to make - for your sake and the kids sake is it better for him to leave or you to leave? Let's assume you decide that he needs to leave. Your attorney can help you file for exclusive occupancy, which may or may not be granted.
3. Not so good scenario - you file for divorce and by his actions / reactions it is clear that uBPDh and you will be able to peacefully coexist in the same house. You try to force him out legally but that fails. Now you are again faced with a decision - do you stay and place yourself in harm's way or do you move out - this could mean depending on family, friends, welfare, etc. What resources are available to you if you HAVE to leave?
Part of what you have to understand as you go through this process is that you need to learn to start placing yourself and your welfare first. Your uBPDh has dysregulated reactions to many things in life. His emotions and issues are not your to own, they belong to him.