My father's stance is very perplexing to me as well. He's a great guy, but when it comes to business, I'm sometimes surprised by the ruthlessness.
My situation is a bit different: My grandfather was killed in a a car accident by an extremely over-worked trucker and we get a very large settlement, millions, out of it. Terrible tragedy. My grand-mother was severely brain damaged, basically lobotomized and has to live with help.
This was in the late 90s.
Ever since, the amount of mis-handling, under-handed dealings, and outright stupidity of my aunts in regards to this money has been astounding. Together, they managed to piss away ALL of the money and pull in a fair share of debt in the meantime.
My parents were more in your position: On the outside looking in, not wanting to throw down legally with family members. Waiting and hand wringing and hoping for the best go them nowhere.
In the end, I got to work 40 hours a week and go to night-school though college, when REALLY, the entire family should have been comfortable and highly educated for an entire generation.
It's been battle-royale, lord-of-the-files for years on end. I tell this story to elucidate you on a very specific point: Just because they're family does not mean they are going to watch out for you. OR, they can just simply be not as intelligent as you are, and make decisions that seem rational to them.
Or they can lie to themselves, and construct a false narrative where they are the good guys, and you are the bad guy. I suspect your father has written your contributions out of his mind, and replaced them with his own.
People see the dollar signs and lose sight of what's important. I've since just forgiven everyone and let it go. That's the decision you have to make, and make it quickly: Drop it and be on good terms with your family, or get a lawyer and quit kidding around.
edit: I'll also update that I struggled with this for years and years. What finally lead me to acceptance and living a much happier life was therapy. Talking with my therapist about the decisions people made, the greediness I saw, the irrationality of the decisions, and the betrayal of my family members.
Talking through it, processing it, and contextualizing with my therapist was enormously helpful.
No matter what the legal situation is, emotionally this is your company as well, and I can't imagine how hard it must be to stop working there.
Talking with an objective outsider might give you some perspective on how best to set boundaries, to be involved but still respected and properly valued for your work.
Although "snake" is a strong word, it may be apt -- it does seem that your father continues to use your emotional attachment to the company as a bargaining chip against you.