Add teachers by making the music/art/other specialists classroom teachers...also by distance learning the high school (allowing for larger class sizes), you may be able to make some of the surplused high school teachers into classroom elementary teachers. Also, put some tents outside for more space

I know it will "suck" for both teachers and students, but it is better than nothing imo and meets most of the goals:

1. Kids in school
2. Parents being able to work
3. Maximum safety

That being said, I dont know how effective of a teaching environment it will be because teachers wont be able to teach the same way (i.e. they wont get close to students)