Thanks for your question on Healthcare Magic.
I can understand your concern.
Tuberculosis is an infectious disease.
It is spread by droplets produced by coughing, laughing, speaking of TB patients.
Since your mother in law is having
active tuberculosis, not taking treatment and she is visiting your home twice weekly, so your son is exposed two her and this can cause cause recurrence of TB in your son.
So better to consult give your mother in law face mask for wearing when she comes to your home.
Also give face mask two your son when she is around him.
Also start anti TB drugs in her for healing of tb.
Hope I have solved your query. I will be happy to help you further. Wishing good health to your son and mother in law. Thanks.