Having a place to store stuff is a huge blessing! When our neighbors moved, they stored a ton of stuff in our basement - starting with holiday decorations as each holiday passed (they have a ton of holiday stuff). Out of season clothes (could be a lot now), kitchen stuff you don't use often (good dishes, fondue pot, punch bowl, etc), knick-knacks. You might even consider moving some furniture to your parents' garage.
Maybe you're trying to do too much at once - get stuff out of the house, sell stuff, do projects. Since your parents live so close, could you clear a lot of stuff out of the house, and deal with it later? Normally I'm opposed to handling stuff more than once, but in your case it really seems like decluttering is more of a priority than deciding what you should sell and what your should give away. You can stack stuff in the garage in sections of Keep, Sell, and Undecided.
Is it possible to bring the kids to your parents' for an evening, so you can get the painting done? You should be able to finish a whole room in a couple of uninterrupted hours.
If the chips are down, the buffalo is empty.