This is my best guess, as to how the individuals in the early records are connected.  Any information that supports or refutes this would be welcome.

1. ELSPET ?
sp: ? CHILLAS
  +-2. ALEXANDER CHILLAS (b. before 1679)
      sp: UNKNOWN
     |-3. ROBERT CHILLAS of Mains of Little Endovie (b. before 1712)
     |   sp: UNKNOWN (possibly SMITH, see note 1 below)
     |  |-4. ROBERT CHILLAS
     |  |   sp: UNKNOWN
     |  |  |-5. MARY CHILLAS (b.1751)
     |  |  | sp: JOHN MCKARDIE (m.1790)
     |  |  |-5. ALEXANDER CHILLAS (b.1747-ALFORD)
     |  |  | sp: MARGARET MACKIE (b.1743-DRUMOAK m.1771)
     |  |  | sp: CHRISTIAN RAE
     |  |  |-5. JOHN CHILLAS (b.1753-ALFORD)
     |  |  |-5. ROBERT CHILLAS (b.1749-ALFORD d.1816-ABERDEEN)
     |  |  +-5. WILLIAM CHILLAS (b.1756-ALFORD)
     |  |    sp: JEAN MILNE (m.1790)
     |  |      sp: UNKNOWN
     |  |-4. MARGARET CHILLAS (b.1728-LEOCHEL-CUSHNIE)
     |  +-4. JEAN CHILLAS
     |    sp: JOHN WILSON
     |     |-5. MARTHA CHILLAS (b.1756)
     |     | sp: WILLIAM INGLAND (b.1761-BANCHORY DEVENICK)
     |    sp: JOHN MITCHELL (m.1764)
     |     +-5. ROBERT MITCHELL (b.1765-ALFORD)
     |-3. ALEXANDER CHILLAS of Seats
     | sp: JANET HUNTER (m.1725)
     |  |-4. ROBERT CHILLAS (b.1736-ALFORD)
     |  | sp: CHRISTIAN STRACHAN (b.1746-KEMNAY d.1823)
     |  |  |-5. ROBERT CHILLAS (b.1765-ABERDEEN d.1770-ABERDEEN)
     |  |  |-5. ALEXANDER CHILLAS (b.1766-ABERDEEN d.1821-FINTRAY)
     |  |  | sp: ELSPET SMITH (b.1760 m.1806 d.1845-FINTRAY)
     |  |  |-5. JAMES CHILLAS (b.1768-ABERDEEN)
     |  |  |-5. ARTHUR CHILLAS (b.1770-ABERDEEN d.JOHNSTONE)
     |  |  | sp: ISABELLA COCHRAN (b.1777 m.1795)
     |  |  |-5. ROBERT CHILLAS (b.1772-GREENOCK)
     |  |  | sp: ELISON ANDERSON (m.1792)
     |  |  |-5. ISABEL CHILLAS (b.1779-NEW YORK,USA)
     |  |  |-5. JANE CHILLAS (b.1781-NEW YORK,USA)
     |  |  |-5. JOHN CHILLAS (b.1783-NEW BRUNSWICK,CANADA ?)
     |  |  | sp: MARIA BROWN
     |  |  |-5. ELIZABETH CHILLAS (b.1786-NEW BRUNSWICK,CANADA d.1861-NEW BRUNSWICK,CANADA)
     |  |  | sp: HENRY FROST (b.1774-CONNETICUT,USA d.1827-NEW BRUNSWICK,CANADA)
     |  |  +-5. GEORGE CHILLAS (b.1790-ABERDEEN)
     |  |-4. MARY CHILLAS (b.1740-ALFORD)
     |  +-4. WILLIAM CHILLAS
     |    sp: MARGARET FORBES
     |     +-5. GEORGE CHILLAS (b.1767-NEWHILLS)
     |       sp: MARGARET NEISH (m.1794)
     +-3. ELSPET CHILLAS
       sp: PATRICK REID (m.1723)
        |-4. JOHN REID (b.1724-KINCARDINE O'NEIL)
        +-4. ROBERT REID (b.1725-KINCARDINE O'NEIL)

Notes

1. William Smith in Wellheads was a witness at the baptisms of most of Robert's children and may be Robert's father-in-law.