Hi,
I'll let the experts weigh in on the spots since your able to wipe them off? Sounds like some type of mold. I wouldn't have the monstera's that close to the window, and do you have a fan blowing in the room?
As for putting your monstera outside I'll link you to a YouTube channel regarding pests. I remember when this guys monstera was thriving and now it has Thrips, sad video. You can view his channel to see what this monstera looked like before.
https://www.youtube.com/watch?...
