from my experience, NEVER, EVER use the "lets go 2gethr" tactic! your team mates will ALWAYS stay BEHIND you and not attack foes until attacked. it just leaves the leader vulnerable.
Have your strongest teammate using the "Go after foes" tactic and the ones you want to level up use "avoid the 1st hit". If they wander off too far, use a Rollcall Orb. (buy from the chameleons)
Be sure to utilize the "get away" and "stay there" commands as well, especially when you're trying to recruit a boss, where your leader has to make the killing blow to make them join.
BTW, Mew appears RANDOMLY in the Buried Relic level, from B36 to B98... I was lucky enough to see him at level 42, but he didn't join for some reason (the leader killed him, my party wasnt full and I haven't got large teammates). Maybe he joins at random too... Anyway Mew only appears ONCE each time you enter the level! if you kill him, he won;t appear again until you re-enter.