Hi, I don't have any expert advice to offer here.
The RSPB says the following on it's site:
If a healthy chick cannot be returned to its nest, it will be dependent on humans for survival, and should be passed on to an expert rehabilitator as soon as possible.
Considering these are very young wild birds, I would get in contact with someone who can help these birds. They seem quite young to be hand raised by someone who isn't an expert at it.
Is there any way that the people where your husband works could be scaring off the parents? Not on purpose, but just by whatever work they are doing.
With the clear and close picture you/he has been able to get, it seems close contact is being made to the birds. Is there anyway that the people there are keeping the parents at bay by being so close?
If you can give us as much information on this as possible, that would be helpful.
If the birds aren't being fed, I would call the RSPCA or a local bird organisation for assistance.