Arthritis in general and Rheumatic arthritis is a common ailment and health issue for elders and I by advancing age the problem increases. In your father's case, 17 years means it has become a chronic issue. However the situation can be managed with proper care, proper motion and rest of affected parts under advice and guidance of experienced doctors. External applications of ointments and liniments can give symptomatic relief. You need not expect a total cure nor you need to worry also if proper and prudent care and management is done.
Ayurvedic treatment is preferable for such chronic cases along with the symptomatic relief medicines. Care should be taken to avoid exposure to cold and humid environments. Applying mild heat press by soft pressing dry cloth warmed on a oil less tawa or by a warm iron box on a multi-folded kerchief, can give relief especially on cold nights and cold mornings. That will ease movement. Modern heating pad also can be used if they are convenient and comfortable. Please take care not to apply overheat.
While deliberate strain should not be applied on the affected parts, keeping without any movement is also counterproductive. For arthritis or similar rheumatic problems, 'motion is the main lotion'. Affected part should be given tolerable motion without hurting or injuring. Causing mild movements under the relief of a pain reliever will be comfortable.
In Ayurvedic treatment, medicine to be taken orally will be also prescribed. There may be some food restrictions like reducing or avoiding sour and acidic foods, foods causing gas and acidity, foods causing kapha or phlegm etc. Sincerely following that will help ease the problem faster.
Proper bowel motion is one basic factor for avoiding many illness including rheumatic disorders also. So the Ayurvedic doctor may also prescribe such medicines or life style regime to have normal bowel motion.
Though these are general suggestions, you better show your father to an experience Ayurvedic doctor , without discontinuing any medicines the allopathy doctors has prescribed. Tell the current doctors that you are going to Ayurvedic doctor and tell Ayurvedic doctor about your current treatment. That will be helpful.