I love having a good declutter but I think you do need to buy stuff to help (boxes etc).
Do you have a downstairs cupboard/closet? I would get one of those hanging storage things that fit over the (inside) of the door and put things like sunglasses/bags etc in there. Our shoe cupboard has one of these along with coats, golf clubs, Hoover, ironing board etc.
I keep all my vitamins and stuff in a clear plastic box in the bathroom so I know what I need to take.
For kids stuff downstairs, a toy box that everything can be shoved in and moved to the side.
Can the sofa blankets be put under a side table?
I’d also invest in a nice bookshelf and have sections so normal books, school stuff and the bottom shelf for admin (letters and folders of bank statements etc).
Ask look up decluttering ideas on Pinterest and sites like good housekeeping online, then often have tips for different areas.
Do you have a garage you can keep your outdoor stuff in a big box?
Stuff to sell on eBay is the worst! Mine is currently all over the place waiting to be photographed... when I can be bothered once all that is done it gets folded up and put in a suitcase or bag till it sells.
Good luck!