Sparrowhawks and buzzards will also take in nesting material to add to their nests whilst the hen is on the nest even when their eggs or young are present, but not all Sparrowhawk males will do this as it very much depends of their mates’ temperament some hens being quite hostile and fiery during this time.
Although hens become “egg lethargic” leading up to and during the laying stage staying quite close to the nesting site and will even allow themselves to be lifted off their nest in some cases, but this is something I would not recommend for obvious reasons being the actions of a fool. Whilst other hens will not allow the male to even approach the nest. But then again I have recorded cases of the male delivering food to its mate on the nest or even covering the eggs whilst the female takes a short break something that is “not supposed to happen in Sparrowhawks” as they have specific roles e.g. the female incubate and feeds the chicks whilst the male supplies the food at a plucking post, at least for the first two weeks or so.
I even once witnessed a male Sparrowhawk feeding two week old chicks after the female failed to return being "very unusual behaviour in Sparrowhawks" being something unheard of, at least I have never seen it written in any book.
Apologies for drifting off your specific question Tony but what I am attempting to illustrate is not all birds behave in a text book manner but are simply following instinct or according to their age, experience, and even the particular habitat, this may even be their first attempts at breeding or being quite normal behaviour in this particular pair.
Of course all things being equal they could still be feeding the juveniles from the first brood and sitting on eggs in the second case, birds act as instinct predicts or in this simply be a case of what Aeshna first suggested, but only time will tell has I like to say Tony.
Incidentally, in this case a predator does not have to be large even mice will wreak havoc destroying the nest and its contents.
It depends on what you mean by up and go tony, they will like other birds close to fledging explode from the nest scattering in all directions if they are disturbed by a predator or man which they also see as a predator. But all being well they will be hiding somewhere waiting to be fed by both parents in which the parents feed half each, pretty cool do you not think. I just hope there are no cats close by otherwise the outlook is grim I am afraid.