My father... have stroke last week only it's affect the right leg of him.... how can we perform at home therapy for my father...
Yes. A leg brace can cause the muscles to weaken and atrophy.
It is impossible to provide the proper advice via the internet, but you are faced with the fact that support is needed and required, but by the same token, you need exercise without support. A compromise much be reached that attains both goals.
Overexercising without supports can cause shinsplints and muscle tears, so that is the other side of the coin.
Only you know the limits to which you can perform at. Push them.
look into
www.brainstrokes.com