We were at a party with several other families, people we've been friends with for years.
As it got later into the evening all the kids started getting into trouble, starting fights, throwing tantrums. They never used to do this before. Our kids are 2, 5, and 7 and they were all the worst kids at the party.
One of the tricky things about deschooling is that you can feel like you don't know what to expect from your kids or yourself any more. You got used to having one set of expectations and rules for how to act, and without them it can feel like you're floundering when things go awry. Eventually, you'll have learned a new set of expectations and tools for various situations, but in the meantime... well, it can feel like things come out of the woodwork and blindside you, to mix my metaphors. To me "as it got later" is a giant red flag - because I remember when my kids were those ages. One needed to be able to take breaks from any kind of social situation. One needed to be taken home before things got to the point that he skipped from "this is fun" to "fight or flight" mode - it sounds like your 5yo may have that kind of short-circuit, too, at least right now, and maybe your 7yo, too. That's something to plan for - as in, plan to avoid, whenever possible, by having a sense of when your kid is tired, or overstimulated, or needs something that another kid can't provide.
I don't want to give up these friends as we've crossed so many milestones together but I hate coming away from these events feeling like this. I should also include that these kids are my children's best friends
Don't think of giving up so much as taking a break, cutting back a little. You all need time to transition, still, learn some new skills together. Throwing your kids into situations where they're going to flounder doesn't help any of you, or your friends. Get together with one other family at a time, two at the most - I don't know how many people were at that party but "ten we've known 15yrs" sounds like five couples to me, plus kids - way too many people at once right now. If I'm wrong and it was just a couple families, then no more than one. Keep things small. Skip parties, but have playdates.
When possible, divide up your kids, too - your 2yo doesn't have "best friends" at this point, so don't hesitate to send them to a separate play date or leave them home with a sitter if the elder two are inseparable or have friends in the same family. If you're married/have an adult partner, plan to split up for social things as needed. One of you takes one kid and the other two, or hire a sitter for one so each kid has an adult.
If avoiding parties entirely would have dire social consequences (worse than your kids becoming "those kids" that no-one likes to invite at all), plan to arrive late, maybe, with kids well fed on favorite foods so that there's no sense of "missing out". Maybe attend parties in between other fun things so that it's easy to leave. Definitely only take one or two kids rather than all three - with that age range, they're not all going to like the same things, and there's a good chance you'll be tied up with the 2yo just when the elders need a hand. Avoid that dynamic by not bringing more kids than adults to parties, at least for now. In five years, things will be different.
I came away feeling judged
While I certainly agree with all the adage that "there's no special unschooling world" it's also the case that homeschoolers are a minority and unschoolers a minority within that. So there are some aspects of minority life that are yours, now, and being judged is one of them. If you have any other experience in your life as a member of another minority group, that will be familiar to you, but if not, well, here you are.
People won't understand, or will misunderstand, or will see you through a lens of stereotypes, or will judge you just for being different. You'll feel caught between wanting to explain and being annoyed at having to explain - again, still, really? didn't we just do this? You'll be frustrated to be The Homeschool Family, official representatives of all homeschoolers, everywhere, and tarred with the same brush. Sometimes it will make you a little crazy. The best advice I can offer in that regard is to, yes, get your house in order and all, but also try not to take the mutters and side-eyes and the rest personally. And, because some days that's easier said than done, find at least one home/unschooling friend irl or online you can commiserate with when three people use "the s word" in one day, or ask what grades your kids are in, or want to know how they'll get into college. Again. Knowing it's not just you can make it easier to let that stuff roll off your back.