Here's an explanation I gave in a previous post. Maybe it will help. If it further confuses the issue, I apologize.
A 1-4 family dwelling is any residential dwelling with less than 5 units. 5 or more units make a multi-family unit. The units do not have to be owner occupied. And if you have 5 families living in a 10 bedroom house, it is not a multi-family unit, it is a 1-4 family unit. 1-4 and multi refers to the design of the unit. Was it designed for 1 family to live in or was it designed for multiple families to live in?
Condos and cooperatives are individual 1-4 family units under one roof, each unit has its own deed and individual owners. When you make a loan to someone for a condo you do not have a lien on the whole condo complex, just the individual unit that the person is buying or refinancing.
Take a 50 apartment complex. If the owner of the complex “rents” each apartment then it is a multi-family unit. If the owner decides to make the “apartment” complex a “condo” complex and starts “selling” and deeding the individual “apartments”, they now become 1-4 family units.
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The opinions expressed are mine and they are not to be taken as legal advice.