Sander—do you have a dog?
At the risk of sounding like your New Age in-laws, I can say from experience that I have experienced the healing power of dogs. Taking care of an animal, whether it be dog, cat, rabbit, goat… is good medicine.
I think there are studies about dogs in particular, helping improve the morale of inmates in prisons, and also dogs that visit hospitals and nursing homes and have a healing effect.
I also believe in modern western medicine. I have benefited from doctors and hospitals too. When I need an anti-biotic, I take an anti-biotic. When I need a colon cleanse, I do a colon cleanse.
I hope that you will be able to heal the rift in the relationship with your in-laws. (puppies are good for bringing people together, too. as are kittens)