Forget overpriced Yurts. Tipi tents are good but you loose a lot of 'real' space because of the sloping walls, you retain more with a Bell tent. I've a big Coleman tunnel tent which will sleep eight but if I were you I'd look at getting two, one for sleeping and one as a social area; leave the bedrooms out and you have masses of space...no bending down, no lost space and weather proof. Get just one and the porch would be enough for you.
[video=youtube;cCJA7RCd6Lo]http://www.youtube.com/watch?v=cCJA7RCd6Lo[/video]
£300 including porch...can't go wrong for family/group camping.

[video=youtube;cCJA7RCd6Lo]http://www.youtube.com/watch?v=cCJA7RCd6Lo[/video]
£300 including porch...can't go wrong for family/group camping.