1 - Your cast sequence syntax is wrong which is probably breaking it, you don't need the slash.
/castsequence reset=6 lava burst,,,,,,,,,,,,,,,,,,,,

2 - /targetlasttarget at the end of the macro (specifically last macro I guess if you're using /click so it does it right at the end) will make sure your slaves dont target anything usually. It probably isn't working because the macro's getting stuck on the rogue slash in your cast macro.

Remember, macro's will do everything at once - it will assist, cast, and targetlast target all at once, so as long as it doesn't error out the last thing it will do is targetlasttarget (/cleartarget will probably work too I think?) and if you have nothing targetted then it won't target anything.


Edit - your FTL seem's kinda .. differnet to mine. Surely it doesn't need to be this complicated. I'm not using /click, but wouldn't it be something like:
Lavaburst macro:
/click assistmacro (controlled by FTL)
/cast lava burst

And just set one of these up for every spell?