children fighting over toys

I have a 9 YO DD and 3 boys ages 2, 4, and 6. They are constantly bickering over toys. There are two swings on our swingset, and they fight over who gets to use them (and one swing is preferred for some reason, so they fight over who gets to use it). We have two Frisbees, and they fight over those (they can’t seem to figure out that Frisbees are meant to be played with multiple players!). The toddler wants to do and have everything the others do/have. The boys have mainly shared toys (play food, Hotwheels cars, and Duplos) and they fight over those, particularly the Duplos. DS1 wants to make huge creations with all the “good” pieces (wheeled bases and flat bases, and sometimes the people and cars) and keep them and play with them for days. The others want to play with some of the same pieces, or take his creations apart when he’s built one and temporarily moved on to playing with something else. We have maybe 200 Duplo pieces, about 6 people, 6 or 7 wheeled bases, 3 cars, and 5 or 6 bigger flat bases (the 4×8 ones). DS1 can use every one of these in some of his creations. I do not know what sort of rules to have for sharing these toys. On the one hand it doesn’t seem fair for him to build something when he’s playing alone and then have someone else come along and want to play and him to have to take his creation apart to share, but on the other hand it doesn’t seem right for him to be able to monopolize most of the pieces of a shared toy all day or for days. This comes up with DD too–yesterday she was playing with all the Hotwheels (maybe 30) and DS2 came along and wanted to play. Or she’ll be playing with “her” toys–Breyer-type and other plastic horses and animals and My Little Ponies and a Playmobil set–and won’t want to share anything or only one or two pieces. She has her own toys and not shared ones like the boys, but I do want her to share at times because if she had a little sister her toys would be mostly shared toys too.

All that to say…I’m tired of the bickering over toys, but I don’t know what rules to set for sharing and playing nicely, or what might be effective consequences for not playing nicely. I am constantly verbally correcting and directing them but it is not working, and various consequences I have tried are not working either.