I really feel for you, you are being pulled in 3 directions and pleasing no-one. And your needs and wants are the bottom of the pile. I know how hard this dynamic is, as my DH is not the father of my children, and when the children were living at home, we had clashes which I just couldn't resolve, because everyone seemed to be being reasonable, but I couldn't bear to see my DH and my kids clashing. For eg. my DD was very very messy, which my DH would call her out on. He was right. But she was also right when she said, it's my bedroom, it's nothing to do with you. I would bend over backwards to "solve" the issues and I just felt invisible as a person on my own right!
Anyway, my children are adults now and have both left home, and on the whole my DH and they now have a very good and balanced relationship.
Back to you. My thoughts, fwiw :
You need to set some ground rules with regards to your DD's visits. They sound extremely stressful for you, and not practical when you have your DH trying to concentrate on work. I would suggest you say to your DD that if your DH is working, that you will go to her house.
Re your adult son, I find it extremely hypocritical that your DH was quite happy for you to support him (him being a non blood relative of 38 years old), for FIVE whole years, but, when it comes to you suggesting that you support your own son (for a much shorter time period), that he kicks up a fuss. He may not want to pay half of the household bills, when there are 3 people living there, but fuck me, if I was him I would happily do that and see it as pay back, for the 5 years that you had financially supported me. Having said that, I hate arguments about money, so I would probably point out the above to him, so that he can reflect on how unfair he was being, but then I would pay for two thirds of the bills, whilst my son wasn't contributing. Even that's not fair on you really, because your son living there doesn't mean the mortgage/gas/electric cost more, so it's really only food, isn't it?
Finally, your post concerns me slightly that your DH could be using you as a way to be in the UK, and now you've married him you have exposed yourself financially and have also placed your children's inheritance at risk Have you made a will? If not, my very strong advice to you, would be to make an appointment with a solicitor asap. They can explain to you how you can protect your children in your will, so that if you dropped dead tomorrow, he can't touch your house (for eg). It will cost you under £300 and will be money well spent.