Merging two spreadsheets with same info.

Hello. I have two students working separately on spreadsheets using Numbers. They are both entering similar data; that is, the columns are the same and they're entering information according to the subject headings in the columns. Now I want to merge their spreadsheets and then post in in iCloud so they can continue to add the information in the cloud instead of in separate spreadsheets. How do I do this? Thanks for your help.