Ankle

It depends in what he can do and he can not do. He is responsible to do everything which he can in his Salah, like standing (Qiyaam). If he is unable to do Rukoo’ or Sojood, then he sit in a chair and do whatever he can. While sitting in a chair, Sojood is on a table in front of him, or he can take the Turbah (Mohr) in his hand and put his forehead on it.

Wassalam.

Yes it is permissible to do that and it does not harm your Prayer at all.

Wassalam.

Yes it is permissible for a male Muslim to wear pants below the ankles.

'Wassalam.

If she is praying at home or anywhere, where there is No non-Mahram seeing her, or able to see her, then she does not need to cover anything below the ankles, but if she is praying where there is a possibility of non Mahram to see her, then it becomes compulsory on her to cover her ankles and and the whole foot.

We have got many authentic Hadeeths in this regard. ( Mustamsak al-‘Orwah al-Wothqa and Jawahiri al-Kalamazoo and other books).

Wassalam.