This would not work, a cast sequence only accepts conditionals at it's start, not on any individual spell cast within the sequence. I can't actually think of a good way of making a macro that automates casting Lifebloom on two different targets. At least, not without using up your normal target frame and using /targetlasttarget, which is simply impractical, for completeness sake, I'll still post that option:
This would work through targeting one person first, then the second person you want to use this on, and then simply using the macro, which should switch between these two players and cast Lifebloom on them. Any other healing you'd do would have to be done through a clickcasting mod however.
Another thing that could be tried which might work (Or might not work at all), would be something along these lines:
The Dummy Spell is in there to basically force WoW not to cast a spell, and thus allow it to fall through to the second /castsequence. But I have no idea whether this'll work, it's just as likely to not work at all.
I'd also recommend installing some kind of error suppresion mod if you're going to be using this.