1 mg of Ativan (lorazepam) = ~.5 mg of Xanax (alprazolam); the half-life is roughly the same.
1 of oxycodone = ~1.5 mg of hydrocodone.
In general benzodiazepines greatly potentiate the sedating qualities of opioids (including the respiratory depression)... taking 2mg of ativan + 25mg of oxycodone divided into several bumps over the night probably isn't enough to kill you, but it is generally better not to make a habit out of combining these two classes of downers... although if I'm understanding you correctly you don't seem to be planning on doing that anyway. Ativan is a perfectly fine benzodiazepine to take for coke comedowns, although even though it produces more sedation relative to its other effects than xanax does, 2mg just isn't a whole lot.
The main issue to watch out for with oxycodone is that it's probably America's most counterfeited drug right now, with much of the supply of black-market oxy actually being supplanted by fakes based on various fentanyl analogues of unpredictable potency, although I would expect that to be less of a risk with 10 mg oxy's (usually they're faking higher-dosed ones).
Edit: I also agree with Jekyl Anhydride on the snorting: I wouldn't suggest insufflating the pills if they have acetaminophen in them (like percocet or equivalent generics)... oxycodone has pretty good oral bioavailability, so what little oxycodone you'd be absorbing on top of an oral dose would be more than compensated by the searing pain of several hundred milligrams of acetaminophen burning in your nostrils.