The nest is nearly finished. One of the Eurasian Blue Tits brings some moss in for the nest.
I find this photo interesting, as you can see, one side of the nest consists mostly of moss. The other side is mostly dry grass. This makes me think that one adult preferred moss and built one side while the other preferred dry grass.
I suspect that it is the female entering with the moss. My theory for this will be explained in future photos.