The ability to have several different custom booking forms with different form fields configurations possible in the Booking Calendar Business Medium or higher versions.
Check more about this feature here. Watch it in this video guide

1) At the front-end side, you can define the showing of a custom booking form or standard form, depending on the form_type parameter in the Booking Calendar shortcode. Please check more here https://wpbookingcalendar.com/faq/shortcode-booking-form/

For example, showing standard booking form:

[booking type=1 nummonths=2 form_type='standard']

Showing some custom booking form:

[booking type=1 nummonths=2 form_type='my-custom-form']

2) For correct showing data at the Booking Listing page and in Calendar Overview pages and emails, depending on specific custom booking form relation to specific booking resources, then you need to define specific custom booking form as Default at the Booking > Resources page for specific booking resources.

3) If you are using the booking resource selection shortcode like in this example, then if you want to show the custom booking form for specific booking resources, you need to define specific custom booking form as default at the Booking > Resources page. You will need to use shortcode like this, without the form_type parameter in shortcode, to load specific custom booking form relative to specific booking resources (check more about configuration here )

[bookingselect label='Please select the resource:' nummonths=1 type='17,16,15']

But if you will use shortcode with form_type parameter in shortcode, then system will load for all booking resources the default booking form or custom booking form depends from your parameter:

[bookingselect label='Please select the resource:' form_type='standard' nummonths=1 type='17,16,15']