Section 66. In making mortgage loans on real estate pursuant to sections 65 to 65E, inclusive, a credit union shall be subject to the following conditions:
(1) A person obligated from time to time to make payments under a mortgage, whether as the original borrower or as a subsequent owner of the mortgaged property, shall be or shall become a member of the credit union.
(2) Each loan shall be on real estate situated within the commonwealth or within a radius of 100 miles of the main office of the credit union without regard to geographical location.
(3) A credit union having assets of not more than $100,000 may invest not more than 50 per cent of its assets in real estate mortgages. A credit union having assets of more than $100,000 but not $500,000 or more may invest not more than 70 per cent of its assets in real estate mortgages. A credit union having assets of $500,000 or more may invest not more than 80 per cent of its assets in real estate mortgages.