you will hear often the "rules" of 4sf and 10sf. My experience is they are not a hard and fast "rules", but ideal. But if you give them more room, they will not suffer. But like most people, space is not always for the asking.
If your coop is primarily for sleeping and the chickens are not confined to it and have run of the run, the 4sf inside the coop is more than necessary. Enough roost space is more important. They will fight for the primo spot on the top roost. Try to keep as many roosts at the same level as possible with adequate spacing.
In you 8x4 coop, are you going with 4ft roosts?
There are only so many ways to arrange roosts into a given size coop. My 6x3 can fit total 9 feet (3 @ 3ft). I have had up to 12 birds - too much bickering. Dropped down to 9 birds and harmony returned.
My run is 6x6, expandable to 6x9.
I experimented and found that chickens like cozy nests. So I would suggest making your one double-wide into two singles.