Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
When a parent has dementia, the religious obligation of prayer is lifted from them because they no longer possess the cognitive capacity required. While reminding them is a good deed, it is not a mandatory obligation for the child, especially as the condition progresses through its later stages.
In response to this question, Dr. Yasir Qadhi — the Dean of The Islamic Seminary of America and the resident scholar at the East Plano Islamic Center — states:
If you do remind him every once in a while, that is good, but it is not your obligation. When you have dementia—when a person has dementia—then the pen is lifted from them.
And if you’re able to help out or do whatnot, then good for you; and if not, then it is not something you are required to do because prayer is an obligation upon the person. When the person cannot remember and think of the time, then the pen is lifted from them.
The same goes for fasting. You are not obliged to make your father, who is in dementia, fast. It’s not your obligation to go after him; it doesn’t work that way. So no, it’s not an obligation.
But dementia has stages, and there are seven stages of dementia. All of this I found out when I had to take care of my own parents. So there are seven stages of dementia. The first two or three stages are much easier to deal with, and you might be able to help them fast. But once you get to the 4th, 5th, or 6th stages, then there is no point because there is no concept of time in this regard.
So do not worry; it is not your responsibility to do their rituals in the state of dementia.
Read more here:
Does Dad Suffer from Dementia?
Almighty Allah knows best.