Hi! I'm sorry, too, about your father's pain. My story with OA is, I've had OA in my hips since I was 20 (I was hit by a car at 16 and it developed over time). A chiropractor took x-rays and diagnosed it, and then proceded to help with it and I've been completely pain free ever since (I'm 30 now, so it's been 10 years!). I also am in no danger of having hip replacements, which is a very real danger with OA in the hips.
For your father, I would definitely try Reiki! The Tibetan Sound Bowl massage is one I've never heard of and it sounds fascinating! I also like acupressure. There are certain points in the body that correspond with other parts, and since these points are located all over, the practitioner can work areas that are not painful, but that will benefit the affected areas. Yoga (and possibly pilates) may also help--a lot!
One thing I took for my hips that will also probably help is a natural nutritional supplement called MSM. It stands for some really long name, but I forget what it is. It's available at health food stores. I personally trust the "NOW" brand the most--their quality is decent. Apparently it contains collagen.
I tend to like combinations of therapies. Sure, I never know "which one" is "doing the most good", but I like to look at all the possible causative factors and take a multi-disciplinary approach. I also find that when I do, I get better faster, which is always the main goal, even if I don't know which one "did it". It's also possible that ALL the approaches I try each contribute in their own way, so it's a win-win
Good luck! I KNOW that natural therapies help, and that they can be just as effective (usually MORE so) than western medical options (which are usually invasive, expensive, and not without the side effects, which can sometimes do more harm than good), and I'm fairly certain there's something out there that can help your father. It's just a matter of finding which one or which combination is most effective, and this can vary from person to person or from condition to condition.
I hope he gets relief soon! I'm sure there'll be plenty of other awesome advice. I'm always amazed at the level of knowledge on this board!
Hugs,
~Jyoti