The stairs are definately from Mango-Sims! I found them, they're part of the Galant set, localized in meubles > sets > autres > page 2. You're welcome.
You don't need Pets for this. I'm 100% sure it's a base game object. Fact: I have Uni and Nightlife, I definitely have this endtable. My game doesn't crash when loading with your package, works all fine, but the coffee table doesn't show up anywhere. Tested with CC free game. However, nice conversion, good job!