@7a98d16b09344744 EA released a 64-bit version of Sims 3 a few years ago, one that works in newer versions of macOS that don't support 32-bit apps. (It also works in High Sierra and Mojave on supported systems.) You might need to ask EA customer support to add the 64-bit entitlements, as they're called, to your account, but you don't need to buy the game again.
The issue with Steam is that it only offers the Windows version of Sims 4. So if you own the game in Steam, you can't play it on your Mac. You'd need to unlink your Steam and EA accounts, or else remove the game from your Steam account; and then claim Sims 4 in Origin or the soon-to-be-current EA App.
The version of Sims 2 that's offered through the App Store does run in newer versions of macOS, sometimes with some adjustments. I haven't played it much, but I did have it open and had a look around.
