Capsule hotels are only for the people who will stay alone or his or her same sex friend.
So if you'll stay three or more people together,every capsule hotel isn't available .
If you want to stay over about four people together, it may be interesting to stay Classic Japanese Ryokans. You can find them especially fishermen's rural towns or spa resort areas.
As far as I know,such a towns are found easily in Fukuoka,Hiroshima,Hyogo(Kobe),Mie,Aichi(Nagoya),Shizuoka,Yokohama,and Chiba.
But it may be rather difficult to learn the rules or manners of Japanese Classic Ryokans or Hotels
I hope you to study about these problems.
We Japanese know these not Friendry System ,so we stay rarely stay Classic Ryokans .