Im going to assume you arent hauling a big tent such as the Sierra Designs Bedouin 6 ($360, 18 pounds; sierradesigns.com) on a backpacking trip. Youre car/kayak/boat camping, or something like it. Right? And the Bedouin is great for that. Its a family camping tent thats built more like a backcountry tent, with aluminum poles, high-end fabrics for the floor and fly, and a sturdy design.
Have you looked at Sierra Designs Moken 6? Its also a six-person tent, but has a common" area between two sleeping wings, so has about 60 square feet more space than the Bedouin 6. It weighs about 24 pounds, but can be trimmed to 18 if certain pieces are left behind in fair weather. Price may be an issue: its $550.
REIs Hobitat 6 ($340; rei.com) is a little like the Bedouin 6a single big space for six people. But its a bit larger than the Bedouin (83 square feet versus 76) and has walls that are a bit more vertical, so you might find that those two things make a difference. Its also roughly as sturdy as the Sierra Designs tent, with aluminum poles, tough taffeta walls, and a heavy coated floor. Very weather-proof. And an excellent buy.
Look as well at The North Faces Trailhead 6 tent ($400; thenorthface.com). Its a six-person tent but, at 94 square feet, is a little larger still than the Hobitat 6. It could sleep two people on each side, with an open space in the middle. Its 24 pounds, so a bit of a heavyweight. But that might not be an issue.
Ideally you can find a store that has these tents set up so you can all pile in and try them. But I think any of the three I mention will give you that extra space you crave.