Just remember to pay attention to the "location" tags.  You don't need to know what people are saying in the other room, in order to respond ICly.  And, while I have a habit to try and include everyone, you don't need to.  In real life, there's usually multiple conversations happening in any type of party or social gathering.  It's 100% okay to just reply to one or two people, if it makes sense from an IC perspective.