The easiest way to gain stronger party members other than the obvious hours of grinding through dungeons is a systematic way of lvling in VH.
Since the game allows you to keep your stats regardless of which job you are, and the lower your lvl the more exp. you gain with each player, the best idea for quick leveling is to be on the lowest possible lvls with your entire party.
I want my main guy to be a strong fighter(keep in mind i said strong fighter but not a high lvld fighter)to do this with out lvling the "Fighter" job class too high too fast, i use the other 3 job classes in series of 5's but allocate all my lvl up points towards strength and def for my fighter.
Lvl up Mage 1-5, then Preist 1-5, then Theif 1-5. While going through all these lvls give ALL lvl up points to str and def(remember this guy is actually a fighter lol)
Now when you go to do your Fighter lvls 1-5 you already have the BP gained from the previous 15 lvl ups which means the possibility of having a lvl 1 fighter with about 40-50 str.
This system works for any job class as long as you make sure to keep allocating ALL the BP points towards the members actual job that you intend for them to be.