Importing data to lookup fields

Hi everyone. I have made a fairly basic app for tracking attendance at meetings. The main form is called "attendance" and related forms are "members" and "organizations". What I want to do is import a CSV of attendees to the "attendance" form and have that automatically populate the "members" and "organizations" forms as well. It's very likely that I will be importing CSVs on an on-going basis, after each meeting.

How do I go about structuring this? Also, is there a way to de-duplicate members?

Thanks!