Hey James,
Have you considered configuring "portal branding" feature? It's free, and it would allow you to give your owner a simple URL to remember using your own domain name like:
https://portal.windmillrentals.co.uk
To be clear, that URL does not work yet. I'm just showing you an example of what it COULD be.
You could then put a link to this on your website if you wanted, maybe down in the bottom footer area, where owners/housekeepers can go to click on it and not have to remember anything.
To do this, go to your Account button > Team Access > and look for the below.
