Alright, here we go. This was actually kinda fun, seeing the numbers is pretty cool. To think that a computer does this in only a fraction of a second...
Back to the subject! Our targets are
and
. Standard, full build. Kai'sa's hp: 2033; armor: 139. Brand's hp: 2816; armor: 126.
build:

Our Trynd's stats look like this: 454.9 AD, 2.08 AS, and 12% Life steal (and 100% crit, but that goes without saying)
This is with a fully stacked guinsoo's, which is really the only time you should be fighting. With alacrity, and a stacked conqueror, we're ready to go in. Using our E, Kai takes 214 damage, taking her to 1819 hp. Our fist auto procs sheen, doing a total of 759 damage, kai is now at 1060. Then, we activate hydra for 139 damage and auto again for 630 damage. Kai'sa is now at 291 hp, and our next auto kills her. This took about 1.5 seconds from the first instance of damage.
Now we move on to Brand, with a whole 3.5 seconds if ult left (checked myself and saw that ult actually lasts 5 seconds, not 4). He's already taken damage from our E and the ravenous hydra, so he's at 2333 hp. Our first auto to him is a double guinsoo's, dealing 686 damage, taking him to 1747 hp. After hitting all these crits, our E is back up, and we use it to deal 202 damage, and immediately auto with a spellblade proc to deal 766 damage. The Brand is now down to 779 health. The next auto does another 686 damage, bringing him down to less than 100 hp, allowing us to kill him with one more auto. This took us about 2.5 seconds.
Well, there you are. The math speaks for itself, and speaks against you. There is definitely enough damage to kill 2 high-priority targets, and there's still about another second to spare. The total hp we gain from life steal and a q afterwards is 552 hp, over 1/4 of our total health pool.
TL;DR: Check yourself before you wreck yourself.