The lower your relation, the lower amount of cash you can borrow at any time. The amount you can borrow at one time is based on your current relation with the town you are borrowing from.
This function differs, however from the Bank of Calradia in that each borrowing is specific to the town you lend it from, and the interest rate is specific to the town in question as well.
Moneylenders are exactly that: moneylenders. In order to use the Moneylenders & Landowners interface, you must enter a town, scroll down the the bottom of the menu and select 'Visit the Landlords and Moneylenders.' This page however, serves the purpose of explaining how this function works, and how you you can use it to your benefit. The Landowners & Moneylenders mod by Duh is a continuation of the Bank of Calradia mod by Garnier and Keedo420.