I'm sorry but they sound dangerously uneducated - mental illness is a very real concern for millions of people the world over. And whether it be caused by the devil or not is surely besides the point - it requires treating in the same way that cancer or diabetes requires treating.

Are you meant to suffer for no reason? Sadly logic simply doesn't register with a lot of religious people, and so what starts as an expression of faith can become a very harmful and counter productive means of deluding oneself and oppressing others.

I would encourage you to leave these people far far behind. Seek out your own meaning and truth - just because we're biologically related to people doesn't mean we're obliged to have a relationship with them. In fact if you think about it, science dictates that we're all technically related to each other...so if you wouldn't place familial expectations on strangers you've no need to do so with people you're more closely related too. In short, seek out the kind of people you need in your life; those who can contribute to it positively.

No one knows what lies beyond - but far better to face that uncertainty knowing you led a happy and productive life then feel regret at having lived according to someone elses standards.