If this situation was permanent, I'd agree with you, but it isn't. Only a few years ago, I was living in a two bedroom apt. and I still had a fair bit of my kids' stuff towards the end. They had been in transition, but by then were more settled. At that point, I said it was time to pick up their stuff and find room in their own places for it. And they did.
This time, for the past two years, all of my kids have been in transition at one point or another, and have needed a place to leave some stuff temporarily. By this, I mean that they didn't have residences of their own to live in for a brief time, for whatever reason. In our family, we do whatever we can to help one another out. I don't worry about whether this is an inconvenience to me or not. As I say, this isn't permanent.
However, this time, it's happened several times in a row, so it's been more difficult to get on top of all this. My son has just found an apartment and reasonable employment in this area, so some of this will leaving this week.
As for my gd's stuff, that's mine. I bought it (mostly used) so that my gd would be comfortable here when I babysat her since that would likely be often, given my dd's need to work, etc. I do clean up, but I also believe that children should be allowed to play without constantly worrying about making messes. Sometimes lately, I don't get to that mess quick enough. I'm not as young as I used to be, and I get also get frequent interruptions in the form of company. I'd rather put people ahead of being a neat freak now.
Normally, I am normally a highly organized person and I frequently purge, so that's not the issue. And I do know all about Fung Shei and Chi. I do agree that one feels better in a less cluttered place and one that has better flow and energy.
However, at the same time, I've come to recognize lately that I feel better personally if I don't stress about this. I'm happier being around people, just being around their company and socializing than what I would be if I spent all that time instead staying on top of this clutter, messiness, etc. and not spending the same time with them. So, it becomes a trade-off.
Meanwhile, I do consider what I could do to streamline everything, which is what I always do in every place, since this is an ongoing problem when one lives in smallish places. But, the idea of even temporarily renting storage spaces seems counterproductive to me. If one is storing what they don't use often elsewhere, why bother having it in the first place?
I use everything that is in now in my apartment. I really only have about one half of a small box (if that, now) under my bed that might be considered mementos or memory type of objects, and the rest is objects that I use on a regular basis, or books. And, I've even streamlined the books. I'll likely continue to purge and streamline for the rest of my life as my needs and tastes change and as I bring in other objects that suit my current lifestyle better.
I'm hoping this fall to be able to get a better handle on this, but if I don't... then, I'll do it sometime later. But, I am able to comfortably walk through my place, and when I do clean, all the surfaces are clutter-free. It's just getting this done sometimes and keeping it that way. I'm not as ambitious as I once was either. ;-)
Plus, when I was younger, I was a bit of a clean freak, and now, I no longer care. Years from now, my kids will remember that I was always there for them throughout their lives, but I doubt if they'll remember that my house was always completely tidy and clean when they were much younger.
And, whenever this does affect me personally, then I just deal with it from moment to moment. :-)