all characters with low levels

[clear]

it is possibly to level up my low level characters,brussianlv29,petulalv29,rosa lv22,heriasalv23,guanidialv30,herbert and joshua level34 or just leave the quest in my best character?because if theres a quest that's need 4 party to split im stuck with my weakest characters.

[Cassiopeia]

This is really low levels.
A good place for levelling is the Eastern Lands. It's a random encounter area and at this state you level up quite fast there.
Or go to the Fire Guild and use the trainer there. If you bought Seed Pendants in Mt. Zulle in LF1 equip them, then your characters gain more XP.

[clear]

Or go to the Fire Guild and use the trainer there. If you bought Seed Pendants in Mt. Zulle in LF1 equip them, then your characters gain more XP.

i will try there.