D.B.
I work extensively in food science education and have seen a lot of people get results with cellular nutrition. This can help with Meniere's, vertigo, chronic fatigue, allergies, food sensitivities and many other things related immune system support. (For me, it was bronchitis, arthritis and clinical depression.) But this is not with a few individual essential oils or a little of this vitamin or that mineral. Using single ingredients is hardly ever a wise decision - that's not how the body uses nutrients. So someone who is "low" in (for example) magnesium can't just take more of it and expect results. That "kitchen chemist" approach is excellent for the vitamin/supplement industry and pretty terrible for people's wallets and health. It's a huge industry but it's not like we are getting healthier as a country, you know?
Have you read anything on epigenetics? There is cutting edge science on the long term effects of environment, poor food (processed, commercially grown produce and so on), stress and family history (which are not genetic but rather epigenetic problems). There's only one dietary ingredient so far that is known to benefit this and do epigenetic repair, which has implications for everything from inflammation to cancer cell growth. It's fascinating and extremely well supported by clinical data. There are thousands of studies completed over the last 10 years and in progress through NIH, major universities and medical centers, and more.
His meds may need some tweaking so it's good that he's seeing his doctor again. You can do a lot for immune system support, but again, it has to be comprehensive and it's not an overnight thing. It can take 3 months for the body to achieve balance so I always tell people to work for the long term and to work carefully with someone. Just buying something off a shelf, with no follow-up from a trained advocate, doesn't work. Part of that is that most supplements are in pill form, which is a huge problem for absorption, and some are in pre-mixed liquids, which is also a problem for potency.
Some people do well with acupuncture or chiropractic - again, it's important to find the right practitioner.