Aww….chickadees. Hope they stay! They will build their mossy nest on top of the other one. I’m not sure what happens to your bluebirds. They may or may not come back. If the dees use that box can you put up a second box so the blues can use it if they want? Put one up now and maybe the dees will choose the new one. One the dees nest and lay the first egg you can put a hole reducer on the inside so that bluebirds won’t sabotage there nest.
Tammy