What do they mean by “sealed?” A stamp or sticker over the back of the envelope, issued exclusively by your school.
Can/should I open my transcripts? Noooooooo! Don’t do it! EPIK won’t accept college transcripts with broken seals.
How many do I need? While I ordered four copies from my university, I only ever wound up using one (when I submitted all my documents in the final application stages). However, sometimes during the diploma apostille or visa issuance process they ask for them, apparently. ‘Didn’t happen to me, though.