M.O.
Well I haven't been in the position of having my parents live with me. However I did have to "have the talk" with my parents on several occasions about NOT treating me like an adult. Basically I was sick of them giving me unwanted advice and telling me what to do when they lived completely dysfunctional lives. And now even being married with two kids, my mother constantly has needed to be reminded that SHE is not my kids parent and that if she wants to spend time with them/us she needs to be the Grandma not the Mommy.
Although my situation is different, I think sometimes things just need to be laid out. I never wanted to hurt my mother's feelings and I presented my "talk" that way. I did make her cry, I did leave her feeling untrusted with taking my kids to her lake house, etc. However it NEEDED to be said. Personally I am someone who "tells it like it is" because I don't believe in being fake, dodging issues or pretending to be nice when I think other people aren't showing respect.
You don't say if your parents are not respecting your wishes or simply being too nice trying to help with the kids chores or maybe not being "aware" of how they are imposing or creating more work for you? I think the tone of the conversation should match THEIR intent...if they are trying to be helpful, say, "I know you're trying to help out, and we appreciate that, however..." Now if you feel they are downright disrespecting what you tell your kids as your mother, then I think the tone comes across as, "I NEED for you to respect my decisions with my children in my house. We love having you here with us. And in order for this to work out, I need to be able to run my house and be in control of my kids..."
I have had to do this over and over again with my mother. Fortunately I think she's finally GOT IT. We will NOT be going on family vacation with her anymore since she has pressed the issue of having things "her way" during a family vacation. I have also told her that I respect her feelings and that WE will opt out in the future. I also have had to make certain things clear when it came to MY family...maybe you will need to do the same. That there are times, functions, etc. that maybe only YOUR immediate family participates in. It's not that you don't love your parents, but that you too need some "alone time" especially now that your home is not a personal sanctuary.
It is so generous of you to take them in. Just make sure you lay out some ground rules NOW before you feel like you have no say in how your home is run.
Good luck!