I don't have a 3D printer, can I use a third party service to print them?

Yes, but you cannont make the models public on these sites.

Can I sell the models I've printed?

No, these models are for non commercial use only.

I'm a teacher, can I give these models to my students?

If you only have a few studetns who need models, then yes. however an entire class would need to buy them.