Before you have a Sim request a table, find the action interaction. I believe it's under the Friendly category. Make them a group. This should allow for them to be seated together. I was able to have my five University Teens dine together, just yesterday. However, Let's Dine Out is still borked. While I had one Sim order for them, the group were served their beverages, but their pizza never arrived. I ended up having to cheat them full, before I had them pay their tab and go back to their dorm at Britechester-U. If you want a Sim couple to go out and dine, use the new Lovestruck interaction by having one Sim ask the other to create a date. Hope this helps. I, too, really love sending my couples out to dine. Makes for a fun date.