I found these guys on-line AvilabilityCalendar.com.
The cost of their service is $30 per year (30-day free trial). Looks good and seems easy. Can easily add things like Early check-in, etc.
Recommend as easiest. This link to the source code would appear on the Turtle House and Pelican Cottage pages.
This “pop-up” link would appear on the Turtle House and Pelican Cottage pages.
Click for Turtle House availability
These calendars could be installed on a new page “Availability Calendars”, or individually installed on each property page.