There are so many similarities here with my life.
You cannot force a parent to seek medical advice unless it reaches a situation where they are a danger to themselves and others.
As in my situation, looking back at their history and current behaviour often provides a pattern for understanding why they are how they are. Unfortunately, it rarely provides a solution.
I'm not going to hijack your thread. I came on site this morning to post my latest problem, but decided to catch up instead.
I wish you well with whatever decision you make