I gather of your query that your one child has been diagnosed to have primary complex and is on treatment for that. You are concerned about the risk of acquiring TB from this son to other family members.
Tuberculosis is spread through air droplets, which are expelled when persons with infectious TB disease cough, sneeze, speak or sing. Close contacts are at higher risk of becoming infected. Transmission of TB occurs only from persons with active TB disease (not latent TB).
History of BCG immunisation is important. BCG vaccine gives around 50 - 70 % protection against TB. BCG vaccination is most useful in protecting children as they catch TB easier than adults.
I would recommend you to visit a chest specialist / doctor to discuss this concern and the doctor could check on immunisation history, look for any symptoms or signs suggestive of latent TB or if necessary a chest x-ray. This particular method to screen for close contacts is called CONTACT TRACING. That would help in detecting if someone else is also having the disease in the family.
Everything depends on the certainty of diagnosis of primary complex in that child. If he is having the right treatment, he would become non infectious after 2 weeks of appropriate therapy, if the TB has not been caused by an antibiotic resistant strain.