Filial piety cannot be a one-way street. The elderly has a part in it. They cannot follow their whims and fancies or their stubbornness to continue to dominate over their children and get their own way. You say, "Oh, it is too late. Old people cannot change their ways." Well, that's not true.
Our brain can learn new things as long as we remain alive. It is called Neuroplasticity. Neuroplasticity is our brain's capacity and capability to grow, to strengthened, to prune new and old nerve connections, in a nurturing environment. Even if you have TBI or suffer from early dementia. Check out the work of Prof Michael Merzenich et al. on the neuroscience of neuroplasticity.
In fact, there are many types of physical exercises, hobbies, and computer brain training that can help the elderly and anyone else with a brain to think clearly, focus better, and remember more. One of the clear signs of aging is Brain Fog. Brain fog is characterized by confusion, forgetfulness, and a lack of focus and mental clarity. But all is not lost!
Another brain training program that does not require the individual to do anything (i.e. no tests, no games to play, no diagnosis) is doing NeurOptimal® brain training. It is offered by a local Muslim outfit Happy Brainlab.Sg The person just relaxes to soothing music for 33 minutes. Improvements in sleep quality, mood and emotional regulation, and feeling less stress are just some of the results of this type of training.
We will always be respectful to our elders. Even though they may not be nice to us, we try to be careful not to offend them (yes, it is challenging). If the elder has a difficult personality, it will be tough on the children, grandchildren and those around them. Some older people don't know that their adult children have their own issues as not everyone is transparent. Not every elder remembers or is mindful of all the sacrifices their children have made for the elder.
For our mental health and sanity, we need (to learn) to let go and let it pass. (Train your brain to be mindful). And you are blessed if you have elders who are wonderful human beings.