Hi RobRoy,
My understanding is that you have four lists on SharePoint, the main list Events, and three other lists Homes, Employees, Eras.
On Edit form, you want to specific values from these three tables.
Per my understanding, I would suggest you add connections from PowerApps to all these lists, then add three drop down controls and set the Items property of each drop down to the lists.
e.g. About list Homes, you could set the Items property of Drop down1 control as: Distinct(Homes, Column Name)
Please try if this works for you. If I misunderstand you, please feel free correct me.
Best regards,
Mabel Mao