If the one cousin has been on antibiotics for more than 48 hours, I believe they are not contagious anymore. As far as the one with a "cold" is concerned, I’d be a little more hesitant. Is there some way that they can play without sharing body secretions?! If the "sick" children are very young too, this would be a lot harder, and I’d likely opt to stay home. On the other hand, if you think that you might have a good chance at keeping the sick kids from smooching/sharing toys/ coughing on your child, I’d risk it and just keep an eye on things. Kids will undoubtedly catch colds, and you can’t keep them in the house every time someone is sick, or they’d never get out the door! (and this all comes from a self-proclaimed paranoid mother!) ; )

Blessings