[bigloo]

Depending on his mental illness, I would not take this lightly and would

1) Stay in touch with authorities to make sure you know when he is released.
2) As already mentioned here, pepper sprays may not work well for several reason, one being mental rage.
3) A tazor will always work, no way around this, out bodies are all the same.
4) Check the law, it lethal force is allowed, use it. He may have multiple assaults but you do not want to be the family where he ratchets things up! I hate guns but stuff like this... well there are exceptions to everything and this is one of them.

Batons, whips, sticks, etc... if your folks are not physically able, especially your mom, they are probably not the best solution. I would advise your parents if he is released not to be alone... go everywhere together, garden together, etc.

Good luck man, this is really terrible... a home is supposed to be your safe place.