To have you sims do actions together, start a conversation and then add people to the conversation.
Once you have that group going have your active sim do whatever action like Make Drinks For Everyone. Dance Together. Channel Surf Together.
It will have everyone in the group join that action.. most of the time. They can and do get bored and split off to do something else.
Forum needs a Sympathy option to add to disagree (automatic), Agree (after finding proof of statement elsewhere), Like (not sure what this is for other than sympathy comments to OPs that done a bad), and LOL (at oblivious people posting comments fishing for sympathy).
Comments
Buy a stereo and invite all the guests to dance or listen to music.
Once you have that group going have your active sim do whatever action like Make Drinks For Everyone. Dance Together. Channel Surf Together.
It will have everyone in the group join that action.. most of the time. They can and do get bored and split off to do something else.
Click on the Sim then select Actions, form group then voila! You can do whatever you want as a group. lol.