I'm sorry your family is like this. It must be so difficult for you to get through your day and the stress they are adding to your already painful condition sounds awful. I got out of a bad relationship, I left him because he refused to do any housework to help out at all and complained constantly about the state of our home. He was the one that made most of the mess, too. He expected my son to do all the housework. That is just not acceptable. My son and I have our own place and we are so much happier (and there is a lot less mess to clean. haha) There were other issues too, he was very negative.
I would like to say that you need to take a step back from the situation you are in and take a good long look at it. This isn't always easy to do, but try. If you need to, make a list of pro's and con's. Take a piece of paper and write down the good and bad about how things are currently in your home and your life. Make one column for good and the other for bad and see which column is longer. If the bad column is longer than you might want to really consider what needs to happen to change that.
Please keep in mind that your adult children are both working, as you said. If they have full time jobs, then it is time for them to get there own place. This may sound rough, but let's be honest. If they had their own place, they would suddenly realize they have to do all the housework themselves, because Mummy isn't there to do it for them anymore. It is time they grew up. If they feel they are working and therefore entitled to not have to do housework, they will be in for a big shock, when reality hits and they are on their own. Stop babying them. You may not like to hear this, but you are partially responsible for their behaviour as you let them away with it. Lay down the law, either they help and do their share of the housework or they find their own place. You have raised them to adulthood, you are no longer solely responsible for them. Cut the umbilical cord and let them lead their own lives now. This will work to everyone's benefit. They will have no choice but to look after themselves which will help them mature, and you and your youngest child will have less work to do around the house.
If you husband refuses to help or even listen to learn what you are going through, I would strongly suggest you think over whether or not it is worth staying in your relationship. It can be really scary to even think about leaving when you have been use to being with someone for such a long time, but do you honestly think he is going to come around and change? Be honest with yourself, you know whether or not he has potential to have a change of heart or not. If you know in your heart that he won't get better with how he treats you, do you really want to stay in such an unhealthy environment? From what you have written it seems to me that you and your youngest child would be better off in your own place without the others. You don't have to cut your other children out of your life completely, but they really need to grow up and move on with their lives and take responsibility for themselves.
I hope you find this helpful and I am sorry if it seems harsh, but we are partially to blame if we allow others to treat us this way. We are basically giving them permission to treat us badly, if we don't stand up for ourselves and stop their unwanted behaviour. We are allowing them to engage in negative behaviour and that isn't healthy for us or them. I truly hope your situation improves and that you are able to resolve your issues. Best of luck.