I actually think that's a common plec. Baby bristlenoses are only around an inch long, and this one looks well within the 3 inch range. As you know, they can get up to 60cm in length and have a huge bioload. Will eventually outgrow their tanks and would be better of in a tank that's at least 75 gallons.
As for the sharks, they're unmistakably bala sharks. also known as silver sharks. They can get up to 35cm and need to be kept in schools. You're better off returning them, as they will quickly outgrow their tank and need some tank more like a pond than any regular aquarium.
Snails can be timid at first and tend to get startled when dropped into new tanks so suddenly. I'd say it'll be just fine.
Imo I'd just return the plec and all the sharks. If you're able to, buy from a more reputable chain. I'm assuming they gave you no warning for the sharks, and not properly labelling their fish, from the case of the pleco, wouldn't buy from there if I were you. If they're happy to sack three bala sharks and a common plec on a 13 year old with no advice at all, they probably don't deserve your money.
looking at your plec vs my bristlenose plec, yours has a more “marbled” patterning than I’ve ever seen a BN
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