You can start a conversation with a few of them and then click in some other room and select "Chat Here" or "Sit and Chat Here"
You can also click on yourself, Actions..., Create Group, and then once the group is created click in another room and select "Go Here Together". And you can click on the stereo and "Dance Together", or clicking on cake and "Grab Serving Together" for those goals in the party event.
Or for just one sim who isn't too far away, "Call Over" under the friendly interactions tab.
I'd also suggest in general always locking computers on residential lots to the household only, unless there's a reason you want other sims to be able to use your computers.