Gem Harvest didn't reveal about Gem Harvesting thing but it did reveal that Universe is NOT last name for Greg and his REAL last name is DeMayo before he legally change his last name to Universe.
When Andy try to left Beach City, Steven tries to stop him because he wanted to know about his HUMAN family since he doesn't know much about them.
I think it's interesting that Steven's HUMAN family would be a plot point for this season or maybe Season 5 since his family was rarely mentioned a lot.
I personally think there was a Bad Blood between Greg and his family as it was implied by Andy that when Greg left them behind after getting his own van. The DeMayo Family was kindly falling apart because of Greg.
It could explain of why Greg change his last name, DeMayo to Universe. Is he trying to cut off from his family? Not even Crystal Gems know much about DeMayo family!
Do you think Greg has a very bad relationship with his own family beside his cousin?