So from what I am seeing here....
Small run/coop combo with a fenced area for more space using the chicken wire. Correct me if I am wrong please.
I don't see anything shading the coop but abundant sunshine. Have you cut vents into the coop? It could be quite hot inside with stale air.
How many birds using this coop? If there are more than 4 including your Sebrights it could be they are getting pushed out due to how tiny they are.
Just read there are 4 silkies too....
It doesn't have to be the greatest it just needs to be effective.

You have another coop? Any reason you cannot move them in now?