My advice is not to take the work and not to ask for money again. It's not being given anyway, asking is only making you feel terrible, and the small amount of work is absolutely ridiculous, fancy asking your husband to undercut someone else when they are millionaires. I think you are right to feel aggrieved, the recession has not been kind to us, however my family have helped out without making me feel like even more of a failure.
If there was any chance they would help, fair enough. But I think fixing your hopes on them when they so clearly don't want to help is actually destructive for you, and stopping you working out how else you will get out of this mess.
I think you should put all your energies into getting as much help as you can from other sources. I know being a home-owner is actually worse in this situation as mortgage-relief does not kick in til several months in, and that's if you are eligible. You may have to face the worst case scenario, which is that you simply give the keys back and go into rented accommodation paid by the state. But do you know what, even if this happens, you will get through it, as you have done those times before.
I found it helped to face the worst-case scenario and then think of everything else as a positive on top of that (i.e. better than that scenario). Have you spoken with the mortgage company, tried a mortgage holiday, tried interest only, tell them you simply won't be able to pay. They are very keen for people not to default right now as it makes their balance sheet look bad, so a frank conversation may help.
Have you got any debts? Ring one of the free debt line (charity, like PayPlan, CCC) and ask about getting the repayments for tax credits sorted. I am sure it is not a 'priority debt' and you can write them a letter telling them to bog off and with a small token amount. If you have other debts, get them to negotiate with your lenders, you only have to pay a tiny amount if that's all you have.
Millions of people live on benefits alone, I know it won't be very nice and you won't necessarily live where you want or have the lifestyle you like, but you will survive this, have your lovely husband and family.
I think facing this will help you more than going to your family who seem to be deliberately hurtful or just ignorant of just how bad things are for ordinary families who have done nothing whatsoever wrong. Millions more would be like you too if they hadn't artificially kept mortgage rates low to stop the entire economy collapsing
Good luck with this, I wish you all the best.