I too have been reading this - brings back some memories of a westie I had years ago. Life with him was hard, lived with my parents then and Dad struggled just to open the door to people, yes he would bite, put then was scared like he new he had done wrong, we could never read the signs as to when he would turn.
The bad time started when my Dad died, he started to dominate the house, I couldn't even sit on side Mums bed in a morning to take her a drink, all this when grieving.
Anyway went to the vets and said I thought I would either have to get rid of him or worse. She was wonderful rang a client of hers who trained german shepherds for the police, he agreed to see us, and he worked with him, the main thing was that as a family we had let him take over and he saw himself as pack leader - we had to never let him be on same level with us, so no on the beds or chairs. It helped then when I met OH he sat on rug one day and yes he bit him. So he never did that again. The police trainer even had time stay when we were away.
You always had to be aware, my heart aches for you and hope there is help for you to find.
Julie