First of these's?

Say a list of things has already been mentioned.

How do I refer to an attribute of the first thing in said list?

• "The first-of-these's attribute"
• "The first's attribute"

edit: thanks for the unexplained downvotes, really helpful(!)

This seems to be a pertinent question as I haven't seen this discussed in any grammar or on this site.

When the noun phrase ends with a noun we are quite happy to put an 's on the end. This is often described in grammars as the "King of Spain's daughter" or some similar phrase and is discussed on SE here. However, since the 's can only be added to a noun, we struggle when the phrase ends in a word that cannot be a noun:

the first of these's
the last there was's

I said "cannot be a noun" not "is not a noun" because it is is OK to use a word that can be a noun, even if it is not a noun in the context

Henry the Eighth's

You just have to find another way to say it

the first's attribute
of these, the first's attribute
the attribute of the first of these

You are describing an attribute of the listed item. It's position in the list is secondary to the attribute.

"The/An attribute of the first of those listed." or "The [attribute name] of the first of these."

If they are distinct things in the list then the attribute's position will be clear. "Of the bird, the mule and the horse the color of the wings is the most important."