I think it's really nice you are trying to help your brother, and unflavored may be a good idea. He may like it.
There is the possibility, however remote, that he doesn't want to vape, and is complaining about his juices. Whenever I hear the term "lazy vapor" that is what comes to mind. It's also why, as I got the husband started, I made him do everything himself, and told him I'd give him sites to pick juices after I chose some initial NETs. At the time he was like, "Whhhhy?" and I was like, "If you want to vape, you are going to have to learn how, just like everyone else." I mean, I helped, but I made HIM clean the tank, assemble it, fill it etc., as I feel there is more buy in that way. He's still dual using, but he knows how to vape, how to change a coil, etc. And he does it (just changed his first coil the other day, LOL).
I think my husband could use some more "buy in" since he's still smoking, but the best I can do is tell him it is HIS responsibility. If your brother wants "different" juice, make him "help" you in whatever fashion, even if it's over the phone, "Does X flavor sound good as part of tobacco to you, do you want to try higher VG, it may be less harsh, etc. etc."
Lazy vapers are just that. Too lazy to do the research, and it enables continued smoking. Best of luck, I understand the worry and I wish my husband will stop dual using. But there is ZERO I can do to make that happen, other than continuing to vape myself and be encouraging. Some of the hubby's days are better than others, and I remember that stage.... I don't want him to stay there forever, but ultimately, it isn't up to me. As a very determined smoker, all I can say is that *I* was butthurt enough to change to vaping, but that doesn't mean everyone is there yet.
I hope it works, Rainsong, I'm just saying don't be thoroughly surprised if it doesn't.
Anna