Just read the OP, at first, i was ready to jump in with a big fat YABU, he needs to work bla bla bla. That was until i read that he wants you to move you your mums!!
Is he MAD??? never mind that you are going to need all the help you can get, but you might actually get more help at your mums but that is is different story. I take it this is your first? That little baby will only be a new born baby once - those first few weeks are precious, so precious - WHY would he want to miss them.
Im sorry but you need to have a re think - i totally understand your situation, my DP is a builder too and to turn down work?? madness in this climate, but things ARE getting better. He just needs to be more confident and assertive. So, you are due in 10 weeks? The first contract is for 8? Well assuming that doesn't run over - they ALWAYS run over - that is going to be perfect timing. Then he can have two weeks or more off and do the second contract - if they don't like it, they can whistle for it.
Seriously, there is work out there, but it has to be chased - its being handed to your DH on a plate and he is very lucky, but their terms are not suitable for your family - eitehr the terms of the contract are changed or he doesn't do it.
Other alternatives - does he work single handedly? Does he have people working for him? My DP pretty much works alone but we get people in as we need them, can he not ask a friend to cover or just put an add in the job centre and pay someone for those few weeks - if he prices the job sufficiently he should easily be able to manage this and still make a bit of money whilst he is not physically there.
There are plenty of ways to make this work - i reckon he is just not ready for the massive impact this baby is going to have on him, he will be head over heals and he isnt going to WANT to go to work, believe me.
This needs sorting now.