#1: I too think it's a mustard family plant, but the color seems wrong to be garlic mustard.
#2: Yeah, it looks like a squash of some kind to me.
#3: That one looked like datura to me, but I only really knew it from a weed in my mother's garden, and now looking at them side by side, the leaf's wrong. I'd also disagree with Chenopodium album, which I never knew as anything but lamb's quarters, and definitely not the equally yummy but very different pigweed (
Portulaca oleracea), also known as purslane, which is also different from the third pigsweed, which I know as amaranth. Yes, common names are definitely tricky sometimes. It's a little too purple, the leaf's wrong again, and it's too shiny (lamb's quarters has that strange dust on the growing end, and the bottom leaves are dullish). Plus the growth pattern is different than lamb's quarters, which is usually much stouter and bushier than this. I'd say some kind of lactuca is a pretty good theory, but I can't promise it's not some weird mustard family or solanaceae that I'm not aware of.
Mitch, send us some more pictures of them in flower if you can. They look like they're all getting close to it. We'll do a lot better on the ID with flowers to work with. Also, your general location (which you can change from the my profile tab up top) always helps narrow things down.