Not sure if this is the correct terminology to explain my question, but I have a client on Drupal 7. My client organization is related to another organization that possibly has a Drupal 8 site. There is a content type that is very similar to both organizations, but the other organization has what seems to be a field group of two fields that allows for multiples in the group, as opposed to the fields. I have used field grouping quite frequently in Drupal 7, but can I duplicate that function?
Sounds like the field collection module would fit your needs perfectly, however that doesn't have a Drupal 8 version yet so it's hard to know what the Drupal 8 site is using to do this.
For Drupal 8 there is a sandbox version of the field collection module however I'm not sure how stable it is.
Another possibility is that they have created a custom field for their site that is a combination of multiple elements.
If you want any sort of compatibility with the two sites' data the I would suggest asking them how they have implemented theirs and use that option for your Drupal 7 site.