Can more than 2 adults be feeding chicks in the nest?
Possibly. It has been known. How are you identifying them as different individuals?
Impossible to physically identify them, but they are coming in as the last one leaves. A least 3.
Before eggs laid, 3 adult birds used to roust in the box overnight..
Why do the parents tug at the outside of the chicks neck?
Answered on other thread!
2013 photos & vids here
eff37 on Flickr