I saw your photo site and read your request.
I have a conclusion that your shoebox apartment is already turn up very nice,
so you don't need to change a lot.
What you need is only some system than can fold your bed (usually German brand, I forgot the brand, but I think Hafele has).
so here is the explanation :
1. when your parents has no guest, you just put the bed in normal position (see image 1)
2. when the 4 guest are coming, you have to fold the bed (you have to do it by yourself, don't let your parents do it :D) (see image 2)
3. when the bed already in vertical position (see image 3), your parents can sit in the daybed below the bed, 2 people can sit in the carpet, and the other 2 can sit in the chair in the balcony
4. about the washing machine, actually you can put inside the bathroom, but it's very tight and you have to hack your wall which is I don't suggest to do that. But for mini fridge you still can put below the sink or on the kitchen set top table beside the wardrobe.
5. about the storage for broom, mop, etc. I suggest to buy some credenza that you can put in the balcony (hopefully the apartment management allow it), because if you make another storage inside the room, it will make the room smaller and the ergonomic is not there anymore.
That's my idea, I try my best to make a friendly design for user, not force all the function that user's needed. Hopefully you like it :)