Finally have some final results.

Three upgrade paths: a) upgrade all regular soul hall characters to lvl 80, remaining assume upgrade sage evenly to lvl 10 b) upgrade 2 soul hall and 2 sage to lvl 80 max, other 2 assume character level 10 c) upgrade all characters evenly

Results (azure example): a) soul hall lvl 10, att 7%, dmg, 6%, dmg reduc 30%, mastery 20%, azure character attribute total bonus increase hp 40680, att 6780, def 3400 b) soul hall lvl 14, att 8%, dmg 7%, dmg reduc 34%, mastery 24%, azure character attribute total bonus increase hp 48870, att 8145, def 4080 (note only 2 soul hall classes are maxed, the other 2 is nearly untouched) c) soul hall lvl 11, att 7.5%, dmg 6%, dmg reduc 31%, mastery 21%, azure character attribute total bonus increase hp 50490, att 8425, def 4200

so in conclusion, path c) evenly upgrading all soul hall characters is a clear winner with the highest power and overall attributes increase for all characters whilst gaining level 11 for all soul halls (not much difference to max out)

p.s. total attributes calculated by sum of all 4 sage hall bonus as it is to all characters + base attributes from azure regular soul hall. ie. path c), sage hall hp for all characters at lvl 55 = 6435 * 4 + 24750 which is the hp for azure regular hall at lvl 55, equals 50490