I think there are several issues, all linked, going on here.
I will preface my response with this: if you really do not want to emigrate then you shouldn't do it. It is hard and not to be undertaken lightly, you both really need to want it to work for it do so. It is clear that you don't, so you shouldn't emigrate. And your DH shouldn't try to force or blackmail you into it- that is absolutely not fair to you.
It is unfortunate that you were open to considering a move abroad in the past (even if not 100% sure) as I think this may have given him false hope. BUT, ultimately, if you don't want to go now then that is all that matters.
However, your DH sounds deeply unhappy. That doesn't excuse his attitude towards your mum, which is childish and callous- but sometimes when we are hurt/angry/unhappy, we don't always behave well (a reason, never an excuse). Does your mum take up a lot of your time? Not that it would be wrong if that were the case. I wonder if he feels everyone else's needs (your mum, your siblings, yours) come first and he resents your Mum because of that. I stress again that being rude to your mum isn't right, nor is just expecting you to put her into a care home without a second thought, but if this is out of character for him then I would be interested in what had brought about this change.
I wonder if he has harboured this wish to emigrate or live abroad as an adventure for some time, thought you were on-board (or persuadable), and is now bitterly disappointed- seeing it as a "now or never" and realising his dream is slipping from his grasp? Before it was always "not now, but maybe next year/in a few years", whereas now he knows it won't happen.
It does sound like you have a number of things you are happy about in life- nice area, nice house, happy with your work-life balance (and I do understand that he was in agreement with these choices). Your DH is clearly not happy though. I love my DH and if I really thought he was deeply unhappy and resentful, then I'd want to try and help make things better if this were possible (recognising that sometimes it isn't)- even if it made things not quite as great for me. Do you feel like that about your DP? If you don't, then I think that suggests your relationship is possible already on shaky grounds. Equally, he should be prepared to see that forcing you to move abroad for him would make you very unhappy.
I think it would be helpful for you both to talk about why your DH is so unhappy and resentful. Does he feel that his desires/views are not important to you? Or less important than your need to care for your mum and keep the status quo, which works for you? If so, I can understand why he might feel resentful (even if he isn't right in his assumption that you put these other factors before him). Or is it really ALL about this emigration issue. If you can both understand the issues from each others point of view it may be easier to work out where to go from here.
Equally, your DP needs to carefully consider whether following his dream is the right thing for his family, as opposed to doing something he would like to try. It's a big thing to uproot children from their home and family, to move to the other side of the world without a support network. Has he really thought this through?
Good luck OP, I don't think either of you is 100% to blame.