Normally the broody will know if the ones under her are not going to hatch - my girl last year kicked one out and got up when the last one clearly wasnt hatching after three days. However, if this is her first hatch she may sit pretty longer than necessary even if they are duds. Are there and signs of hatching in the remaining eggs at all - pipping? Maybe a quick candling of them, but I suspect that they are not going to hatch now as such a big gap between. I also think it may be time to remove them from under her and let her concentrate on rearing the two that hatched out. Also, unless strong of heart dont crack the eggs open as I made this mistake and found it a bit distressing seeing the chicks that had started to develop but not finished - but Im a big softie and know some people do like to check to see where it went wrong.