alef - mother over six of the aspirated variants of the double letters

mem - mother over six of the muted variants of the double letters and other stops (eyin, tet, qof)

shin - mother over the other sibilant letters (zeyin, samek, tsadi)

There are nine letters remaining:

רוח אלהים … נ

Two glides/semivowels: yod, vav

Two gutturals: heh, khet

Two nasals: mem, nun

Two liquids: lamed and resh.

But, of all the letters, resh is particularly elusive, as it has traits of a guttural, a double letter, and even somewhat resembling a sibilant (when trilled), a mute/stop (when tapped), or an aspirant when rhotic.