Recommendation: use helper functions to help deal with nesting. Your schema-properties
macro knows how to deal with one level of nesting, and you want to apply that to multiple clauses. It's the same principle as when we deal with lists of things: have a helper to deal with the thing, and then apply that across your list. It helps cut down complexity.
For your code, we can do it like this:
#lang racket
(require (for-syntax syntax/parse))
(define-syntax (schema-properties stx)
(syntax-parse stx
[(_ [clause ...])
(with-syntax ([(transformed-clauses ...)
(map handle-clause (syntax->list #'(clause ...)))])
#'(list transformed-clauses ...))]))
;; handle-clause: clause-stx -> stx
(define-for-syntax (handle-clause a-clause)
(syntax-parse a-clause
[(prop:expr ...)
(make-prop-hash #'(prop ...))]))
(define-for-syntax (make-prop-hash stx)
(with-syntax ([(props ...) stx])
(if (regexp-match #px":"
(symbol->string (car (syntax->datum #'(props ...)))))
#'(pairs->hash 'props ...)
#'(props ...))))
;;; Let's try it out. I don't know what your definition of pairs->hash is,
;;; but it probably looks something like this:
(define (pairs->hash . pairs)
(define ht (make-hash))
(for ([p pairs])
(match (symbol->string p)
[(regexp #px"([-\\w]+):([-\\w]+)"
(list _ key value))
(hash-set! ht key value)]))
ht)
(schema-properties [(name:first-name type:string)
(name:last-name type:string)
(list 1 2 3)])