[Em David]

Two of our hens eggs have started to hatch, today, but both have died whilst hatching. There are two more due to hatch tomorrow but can anyone tell me were i've gone wrong as really don't want to lose the next two.
Hen is sitting in a converted wooden playhouse, so has plenty of air and space.

[bantam novice]

I am so sorry to hear about the chicks 

I am not an expert but I'm sure someone with more experience will be along shortly to advise you. 

In the meantime did the membrane of the egg seem very dry?  That makes it harder for the chick to break through.  How long had the broody been sitting on the eggs?  The average is 21 days (start counting day 1 from the day after she starts sitting). 

Well good luck and don't let this setback put you off trying again