I am amazed at how many people store things for other people. This may be a very kind gesture for a short time, but make sure there is an end date. Their clutter is having an impact on your home and your life, no matter how big or small the pile. Give them their stuff back and let them take responsibility for their own things.
A great way to disguise the hard to tidy items, easily accessible items like car keys, note pads, pens etc.
There are two ways to go through life; gather up everything in sight in-case you might need it someday. Or just trust that you will find exactly what you need when you need it. Guess which one gives you more freedom of daily living and less stress? Which do you choose?