Is it a foregone conclusion that your P's have to visit, and/or visit at your house?
Other options: -- Wow, we'd love to see you but this week doesn't really work for me. Is there another time in the next week or two? -- How about we meet you half way and have dinner and a movie out? Or a hike and brunch? -- Wow, we'd really love to see you but I'm not sure we're up to hosting, how about we come over and bring dessert? -- Hey, I know I said OK but I guess I felt put on the spot and panicked. I need to ask you to let me off the hook so we can find another option that works for everyone.
Do not be afraid to make your quality time with W a priority right now!!!