I'm going to assume your being honest and adress yoru concerns in the order they are given. I hope that this is helpful.
1. Your brother thinks illusions and occult things are cool, he may be a magical practitioner, but that's if you think that's evil you've come the wrong site
2. Your brother is a lucky dog. He's just smart and probably has a really good metabolism. He avoids all foods with salt so his meals are probably super healthy and unprocessed leading to less body fat and more nutrition
3. Lots of people are of the opinion that religion is bogus. I can't stand preachers myself. They are full of judgement about everyone but themselves.
The Christian church has frequently behaved in oppressive ways historically and your brother may feel that the church dilutes tha message of god and that your relationship with god should be personal and based off scripture. He may believe in god just not religion He's also likely gay so he wouldn't be a fan of the church
To wrap up this point, your brother has opinions, like a human being.
Also man alone has god's gift of free will. If your brother is a demon he'll only hurt people because god asks it of him. I've always wondered whether god and satan have an inside deal going
4. Your brother may be a drug dealer or have an illegal source of funds
5. Your brother is likely a homosexual.
6. Your brother becomes legal at the age of 18 and is independant of your parents. By your own description his values don't seem to match up with your parents'.
7. Your brother has a medical issue with processing salt, he's not excreting enough salt in his urine and devolops excessive sodium symptoms that include diarrhea, abdominal cramping, nausea and vomiting. Another explanation is that he is repulsed by the taste to the point of nausea
8. Demons in the christian sense have horrible issues with religious iconography, your brother wouldn't be able to stand hte image of jesus if he was a demon. He is probably practicing occult stuff and isn't really interested in telling you. Here is my explanation of what might have happened
candle light produces many shadows, his eyes may have appeared black because they were in shadows
That technique to knock you out sounds like stage hypnosis. If you were in a nervous state it would be very effective. Your brother practices stage type magic so its quite likely. It also explains how you kept your memories. Magic has ways to make memories fade, but inducing amnesia through hypnosis is famously unreliable. Hypnosis can also cause people to invent terrifying memories
Learn a few protection spells or carry holy water, whatever makes you feel safe. I'd recommend confronting him about his practices without being judgemental. Tell him that you want to understad what you saw and that you will keep it private and love him either way. If he tries hypnotising you you should learn to avoid induction. Keep yourself aware and distract yourself with different details in his room. You can't be hypnotized if you don't want to!
I hope that many of my ideas do not prove to be true as they are simply aweful. I'm also pretty sure that your brother doesn't sound like a demon. If you want to learn more about your brother ask him and not the internet.