SoSad2Bad....I don't know the details of your situation, outside of this post....but, from what you say, I can wager that your kids know much more than what you think they do. Parents almost always underestimate what kids are aware of. They may not know the reasons for things, but they know when something is wrong. And, especially, if he is "picking?" on t he kids.
Can I assume that the 8yr. old is the oldest child?
Make the explanation age appropriate and simple, is my suggestion. They will not ask you about complex dynamics of YOUR relationship.....
Kids take their security in short increments....like...where are we going to sleep? Can we take the dog? Can we order pizza for dinner?.....
They may feel grateful that you are m oving.....
It is typical for kids that they may take a while to voice any questions or concerns...later, a little bit at a time.
They will take their cues from you....if you don't project lots of anxiety and insecurity...they will feel much more secure...
It sounds like you and the kids are in a bad situation....it is always best to leave a bad situation than to stay in it...especially when children are involved.....