It's not just Scientology but Scientology does seem the most successful of the late 20th Century cults that do this to people.
Lots of people I know are in intractable situations like this, not brainwashing cults but situations where escape momentum is not even being sort let alone achieved.
The only advice I can give you is you can't fix other people.
You can only fix yourself and hope others are moved by your example.
If Scientology gave you at any time a false sense of stability through ritual or being part of a community take ownership of your stability by inventing rituals of your own or joining communities of your own choosing.
It's only human to want to seek acceptance from your own kin but they are caught in the same quicksand you have narrowly escaped from. If you don't want to go under again you have to let them come to you. Make it clear to them that the lines of communication are open but don't seek them out in this passive aggressive manner.
There is a lot to live for. You need to define your own tastes, your own path and make your own connections. The Hubbard cash cult at the moment makes all those decisions for your family members and you know the cost and you know it's not for you.
Maybe they will see it's not for them either when they see you succeeding on your own terms. Faltering outside of the cult just reinforces their delusion that Scientology is the panacea. You are enabling their enslavement if you are seen to not survive without the Scientology scam. It's not called a confidence trick for nothing. If you immerse yourself a life of your own design you will bring the boon of genuine confidence back to those you seek to liberate.
All my hopes.