MANY years ago, back when I had time to watch Oprah, she had a guest stress management "expert" who taught me how to say NO! to my friend who was always making "passive agressive" requests to me ON THE PHONE.
This person said to STAND ON ONE FOOT (which gives you the feeling of urgency...because you're not allowed to let it down until you say NO!) Then say, "I am UNABLE to do that right now...I have to go right now...I'll call you later" and HANG UP! IMMEDIATELY!! Not "can't...can't right now...or MAYBE later". UNABLE is the trigger word! DO NOT JUSTIFY your reason. You don't have to be On-Call for the rest of the world! After you hang up, you say out loud, "I just put my foot DOWN!" The first time you do it, you'll feel incredible guilt. (wink) Then, when you discover that Life went on without you, you'll feel relieved - totally - of that burden!
I'm sure you've done research, including the "Rescue Triangle" that's mentioned in the "Co-Dependent No More" series, and how the CHAIN must be broken.
If one considers something to be an Unreasonable request, one must declare themself LIBERATED FROM THE OTHER PERSON'S CONTROL.
I also like Dr. Phil's theory of OWNERSHIP. Who's problem is it? If it's not mine, I don't want it. I have enough burdens to carry, thank you. "I am UNABLE to carry your problem at this time."
The trick is to prioritize. Discover what is IMPORTANT, and what really ISN'T!! (Choose your battles. Is a perfectly clean room THAT important? Or can you live with a "safety path" between the bed and the doorway?)
Discover what NO really means. Does it mean Not Now, or Not EVER? A cookie request could be "Not now, but after dinner." A peanut butter cookie to an allergic child means NOT EVER!"
Jumping on the trampoline in the back yard (supervised) is a Not Now...jumping on the furniture is a Not EVER.
Yes transfers control / power to someone else. It gives permission. NO! means "I'm still in control of ME!" NOT THEM!
Remember, you don't really ever control another person...just their behavior...or the situation.
Good luck with your book. Let me know if you need anything else. I'd be glad to help!