If two objects are declared in a single line, in which order are they constructed?

From 8 Declarators [dcl.decl] 3:

Each init-declarator in a declaration is analyzed separately as if it was in a declaration by itself.

It goes on to say

A declaration with several declarators is usually equivalent to the corresponding sequence of declarations each with a single
declarator. That is
T D1, D2, ... Dn;
is usually equivalent to
T D1; T D2; ... T Dn;
where T is a decl-specifier-seq and each Di is an init-declarator. An exception occurs when a name introduced by one of
the declarators hides a type name used by the decl-specifiers, so that when the same decl-specifiers are used in a subsequent
declaration, they do not have the same meaning.

You can say that they are constructed from left to right.