From your post, OP, it seems that your DH stopped working when his Mum died in Nov 2014, and hasn't worked since. of course I have every sympathy for his loss, but this is not normal OP. We all have to deal with the loss of loved ones at some points in our lives, and whilst we all need time to grieve, (and some employers are better than others at recognising this) life does have to go on and we still have our responsibilities - work, parenting, etc.
Things will not "sort themselves out" as he seems to think they will.
He appears to be sitting around playing games all day, not looking for work, while you do the majority of the childcare. He may well be depressed, but if so, he needs to access appropriate care and treatment. Can you possibly have a word with the GP? Of course the GP cannot tell you anything about your husband, but you can tell the GP your concerns, and how your DH is at the moment. If he is depressed, not only can he access help, but also possibly extra payments while he is unable to work. Is he currently claiming JSA? (In which case he should be actively looking for work...) What work did he do before his Mum died?
In the meantime, you need to sort out what is going to happen. I think you have to give him an ultimatum. Either he finds work, or you go back to work and he does all the childcare while you are at work, plus a decent share of all the household tasks. If he claims to be too unwell, then tell him he needs to carry on seeing the GP and get himself fully investigated and sorted. You also need to agree some kind of repayment plan with your Mum, even if it is a tiny bit each month.