can be a big problem in your household. Please seek appropriate preventive treatment of the twins.
I am really sorry that your children are having so many problems. The five-year old child should be treated aggressively for a week; if there is no relief at the end of that, you should get him admitted for bronchoscopic lung aspiration to get the organism from inside the lung directly. Treatment will depend on the results of the culture and the sensitivity patterns of the organism grown thereof.