I'd stay away from all those projects! Your vacation is supposed to restore you, so unless cleaning and painting really make you feel awesome, I'd ignore it. It doesn't seem like your husband and kids are doing them! LOL. So they are relaxing and having fun, but you're not.
I'd go to the library and get myself a few good books. I'd sit out on the deck (and not notice that it needs to be painted!) and sip iced tea and maybe a lunch I picked up or one of those salads I made ahead of time. I'd take myself to a noon movie and enjoy something bad like candy or popcorn. I'd go browse at a store I've admired just to fantasize - home decor, gardening, whatever you like. I'd go to a local art museum or science museum, and enjoy doing it without making sure the kids were interested. Many of them have courtyards or patios and you can take your salad with you. I'd go to lunch with a friend and make it a grown-up restaurant instead of a kid-friendly place, and I might even order a glass of wine! I'd go sit on a beach or at the lake/pond, with a picnic, a chair, and a good book. I'd go try on some new clothes or maybe treat myself to a new bra or two - I'm always the one who goes without, and I'd use my stay-cation (and all the money I'm saving) to do something about that!. If I didn't feel like shopping, I'd get a massage or a manicure, whatever is a treat for me.
At night, I'd rent a few movies that my child and I could enjoy together, go out for ice cream, play mini golf, or do anything that's appropriate for the child who's home with you that wouldn't be enjoyed by the one who's visiting the grandparents. I'd create some special time with him.
I'd cram as much of that 10 hours of business time into one or two days so I'd have some full days free to really rest up and reinvigorate my mind!