May depend some on what sort of turkeys and to what age. But many books say 5 sqr feet pir bird.
That is sheltered space for roosting so if your coup is 24 sqr feet likely about 5 would be max. if you looked at the whole pen as their space then you might be able to go a few more. If you are just growing out BB meat turkeys for 12 weeks or so you might get away with a few more than if you were keeping them longer term.
I have 16 turkeys in a 16x8 tractor with half a dozen chickens, it is fairly full and have seen a little feather picking.