Light-hearted romp nearly kills my players

So, to start things off, this was my first time DMing an actual campaign, but I had DMed some oneshots for this same group.

Party consists of: Me (the DM), C (Aasimar Soulknife rogue), G (Halfling druid), M (Stone giant bard), and J (Harengon monk), all level 7 or so.

Campaign setting: fancy high-class event where the party was supposed to guard a family of nobles, lots of disguised baddies.

Big bad got taken down the previous session in an absolutely hilariously pitiful fight, C and J sustain some damage but not much. C, G, and J, who were the ones taking care of the BBEG, head back to join with M, who was guarding the family. No time to rest and recover.

Suddenly, six assassins discard their disguises and engage. Two are positioned on chandeliers with only ranged attacks, the rest are on the ground with only melee attacks.

G summons 8 wolves and steps back, C gets on the chandeliers to engage with those assassins, and M and J focus on protecting the family.

Now, if you don't know, assassins, if they land an attack, could potentially deal 7d6 poison damage, or half as much on a save. Most times, their attack lands because for story purposes AC is reduced, and my players end up failing some saves. I nearly end up killing our high-hp bard and our rogue, at which point I realize I glossed over something: assassins have multiattack.

I decide that I don't want to torture my players and stick to single attack assassins. Players dispatch the enemies fairly quickly considering what I put them up against, one guy gets killed by getting pushed off a chandelier and then landed on by C jumping off the chandelier, and we all share a good laugh.

Moral of the story: read things carefully before throwing your party against a very deadly set of enemies!