No.
Even if you assume your original post where Fighter = 12 hp, Cleric = 9 hp, Rogue = 8 hp.
Everyone rolls initiative because you are initiating combat even though they're asleep. You cast sleep spell in the first round without opposition because you get surprise in that round.
If you roll high enough they're all asleep. If you don't, those that you didn't get would get perpception checks to wake up.
Great, now you get a free attack on your party members who are asleep.
You still have to roll to hit. Yes, you have advantage, but you can miss the attack, even on a sleeping target.
IF you hit with a... firebolt. You'll probably kill the rogue or cleric. Maybe depending on the dice. If you dont', they automatically wake up and act in the initiative order that was rolled earlier. They might go before you.
Anyone (probably the fighter) who didn't get slept by the spell, gets a chance to wake up each time you cast a spell whether its on them or not. If they wake up, they act on their init. If the fighter wakes up, you probably lose this attempted murder.
Is it possible? Yes. Is it guaranteed if you play how the rules are actually written? No.
As others have pointed out, it's not too powerful, even if you want to PVP and happen to be a serial killer wizard.
Plus, good luck playing in that group anymore!
But wait, there's more!
That human fighter or the human rogue, took Alertness with their bonus feat. They get +5 to their init, so if you dont' sleep them there is a great chance they go before you.
Better also try this before someone in the party gets a Weapon of Warning. You'd wake them all up immediately when you became an enemy by targeting them with hostile intent.