some ideas
Make your room and any space that is yours in a common room work to your satisfaction (e.g. your bathroom shelf).
Keep talking enthusuastically about your process and the results you are getting. Talk as if you are telling friends about a vacation trip you have been on-no long monologues but lots of references to what you did and what your experiencing.
Show them that it does not hurt to throw stuff out that is unneeded. Talk about the results (" I got rid of my odd socks and now have I have room for all my pjs in one drawer).
Provision yourself adequately so you don't rely on the packrats for odds and ends you need. Label yourstuff and keep it in your room.
Offer to help box up items and put them in a storage area-tell them you will take a picture, put it in a book, and label the box so they will know where to find it. You can probably get the okay for this for out of season decorations, if you are polite about it.
Gradually start putting like items together or create racjs or holders for items at point of use.
Help them have a party with a good long lead time. and make a time line.
As you gather like items, it will become apparent that they have unecessary duplicates--some of these just need to get used up, others you might be able to make dissapear if they truly don't know how many they have.
Label necessary duplicates by the room they belong in (kitchen scissors, office scissors, laundry room scissors).
Ask if you re-arrange some small area that is mainly aethetic and show them that less is more.
Throw out the junk mail immediatly-put a good trash bin by the door.
Collect manuals and directions and start putting them in one place (unless you like to file them by items) OR neatly attach them to the object or create a way to store them near the object.
Unless they have a green house or similar, they don't need to save every container-figure out what is reasonable for their needs and each recyling day pitch a few until you get down that number.
Give them a gift of paiting a room (by you or another) and then start clearing that room out-start with the easiest.
Good luck!
