Zaid Alsalami, Shaykh Dr Zaid Alsalami is an Iraqi born scholar, raised in Australia. He obtained a BA from Al-Mustafa University, Qom, and an MA from the Islamic College in London. He also obtained a PhD from... Answered 2 days ago
Bismihi ta'ala
If they are incapable of standing up, even with leaning, or prostrating on ground, or if they do so, there is unbearable pain, they can use the chair to perform their acts of salat, based on what they can do normally, or cannot.
And Allah knows best