I'll get back to the Jarda vowels after I have a better idea about how 
the consonants changed from Proto-Jardic to Jarda. Basically consonants 
were palatalized before /i/ and labialized before /u/. (If there was /ü/ 
at that time, it might have palatalized some consonants and labialized 
others, but I think /ü/ came later from /iu/ or /ui/.)

Velar and alveolar consonants (except for /r/, /ɬ/, /ɮ/) were affected 
by palatalization. (It's possible that Proto-Jarda didn't have /ɬ/ and 
/ɮ/ to begin with.)

*n > ņ [ɲ]
*t > ? (maybe č > ś or ķ)
*d > ? (maybe ǰ > ź or ģ)
*s > ś [ɕ]
*z > ź [ʑ]
*l > ļ [ʎ]
*k > ķ [c]
*g > ģ [ɟ]
*x > [ç] > j
*ğ > j

One mystery is the origin of the initial clusters /śl/ /śṛ/ /źl/ /źṛ/ in 
Jarda. It's possible that they come from palatalization of *sl, *sṛ, 
*zl, *zṛ before /i/, but then what happened to *kl, *kṛ, *gl, *gṛ? You 
don't find /cl/, /cɻ/, /ɟl/, /ɟɻ/ in Jarda.

Labialization affected labiodental and velar fricatives, and possibly ṛ 
/ɻ/. That /ɻ/ is an oddball consonant in Jarda. Maybe Proto-Jardic had a 
whole series of other retroflex consonants like /ʈ/, /ɖ/, and /ɭ/.

*f > [ʍ] > w
*v > w
*ṛ > w ?
*x > [ʍ] > w
*ğ > w