As stated, check your school's policy first. Some states have more wiggle room than others. Private schools get to make their own policies.
If your school is fine with it, then I highly doubt they will request that the teachers give the students work ahead of time. Some teachers still will - or give as much as they can. That is a long time for a teacher to be able to give all assignments. Often teachers prepare their lesson plans just a week in advance as so much changes. Even then, changed are often made. So, expect that at least the 7th grader will have a lot to make-up upon returning. Once the vacation is approved from the school, then have your 7th grader approach the teachers about getting work. He/she can mention it now and then should mention it a full week in advance. It's up to your child to request the work. (You can request it for the 2nd and 3rd graders though).
As for Halloween, it is usually a normal school day in middle school. Just as much gets done that day than any other day. That's even true in some elementary schools.