G’Day from down under
Bits and Bobs 
Welcome!
Rule of thumb with the premanufactured 'kit' coops is to halve what the retailer advises they can hold. So if they say 8-10 chickens, you are looking at 4-5 and as you have found, even 4 might be pushing it.
I battled with 1 x kit coop for a while and then joined 2 together with extensions etc and then just gave up and built a big one.
Each large chicken requires 4 square foot of coop space, 10 square foot of run space and 2 foot of roost space.
You might find this forum of assistance:
Coop & Run Forum
You might also be interested in downloading this free e-book
My First Year With Chickens
I do hope you enjoy being a BYC member. There are lots of friendly and very helpful folks here so not only is it overflowing with useful information it is also a great place to make friends and have some fun.
Personally, I have found the
Topic of the Week articles a great resource and a one stop shop for questions which may have already been discussed within the BYC membership group.
If you would like to share pictures and stories of your flock, you have come to the right place. BYC’ers never tire of these and do not back away slowly or commence eye rolling when the photo album or home videos come out
Best wishes for a bright and cheerful Christmas and a Happy New Year!