Should you? There is no obligation to be. But I would be rather miffed. It seems from this post and your other that your family seem to have different values. You look after your mum, problem solved. For them anyway. They probably don't think too deeply into it, because it is just easier for them to live their own lives and leave you doing what you do.

Can you ring your sister and ask if she could come down for a week or so and give you some time to take a break? Lay it out plainly for her - you have cared for your mother for many years without a break and would like to have a bit of down time.