I'd suggest splitting your macro into two spearate ones. The first one would be bound to a key (e.g. F) and the other would be your normal spell.

Code:
 
/assist maintoon 
/focus [exists,harm,nodead] targettarget
and

Code:
 
/cast [target=focus,exists,harm,nodead][] Lightning Bolt


This means that your followers aren't going through the whole target switching rigmarole every time you cast a spell (should reduce number of problems), it also means that all your toons will 'lock on' to a target which means that your main can target someone else (hopefully fooling your opponents into wasting their healing) while you DPS with focus.



Please note that I'm not a PVP or arena player (although I do play on an RP-PVP server)