Air purifier

So I’m in desperate need of something to get rid of all of these damn germs. So basically long story short, we have split custody of my step daughter and every and when I say every I mean every single week that we get her shes always sick, and so I always get sick too, from the constant coughing never covers her mouth(constantly trying to get her to at least do that) and sneezing and swallowing her snot instead of spitting it out, we give her medicine she goes home and her mom gives her spoons of honey instead of the medicine which is clearly not working for her bc she always gets worse from it, and so she comes back siper sick again every single time. Okay so now the baby is about to be born and I need something to keep the air clean for him. I constantly clean the room clean the sheets but it all goes to waste bc immediately the constant coughing and running snot not washing hands and touching everything bit covering her mouth starts and then everyone’s sick again. I was thinking maybe an air purifier might help keep the baby from getting sick I really don’t know it’s such a frustrating situation.