I don't think treating them as children works unfortunately. In conflict resolution there are three actors, parent, child and adult. It sounds like you need a family meeting and you need to keep really calm throughout. As a family you need to work out expectations of everyone (including yourself) to live happily. It takes a strong character not to revert to being a parent but if you do then the other actor in the resolution will revert to a child state when they do not have the emotional maturity to remain an adult. It's fascinating stuff and it's something that a child psychologist talks about that I listen to.
If you stop thinking of the older ones as your children and actually cohabitants of your house it changes your perspective. If their room is untidy, it's their room. It's their choice. The rest of the house is shared space and there are expectations.
Think about how you'd feel if someone told you how to keep your personal space. Your teenagers will only learn responsibility by having some.
Now clearly if they've left uneaten food in their room that may attract pests but in your family meeting you can discuss consequences. Same as not washing clothes etc. You can say at your meeting that clearly they wish to be independent from you and therefore you as a family need to move towards a new dynamic
It may also mean that you have to divvy up the shared space so crockery, cutlery, glasses for you and the younger one and then they have their own stuff. It will eventually work. Some of this is about accepting that they are immature grown ups... And so they need to start behaving like grown ups