SH4 - This one is the most accessible.They're both on MyAbondonWare and you can find the ISOs to the PS2 versions on. The PC version doesn't have a remastered mod, but it's a strong port nonetheless. Perhaps the simplest (and most recommended) way to access them is to download the PCSX2 and emulate the PS2 version on your PC, or download the PC version with the Enhanced Edition mod. If you can find a physical copy, the original X-Box version is backwards compatible on modern X-Boxes.

The HD Collection is on PS3 and X-Box 360 (physical copy only, and recently removed from PSNow on PS4), but it's a bad port in itself.

SH2 - Not really available anywhere in decent quality.

Silent Hill Downpour -> You can play it on PC with the PS3 emulator (RPCS3) or by backward compatibility with Xbox Series.

Silent Hill Shattered Memories -> You can play it with a PS2 Emulator, a PSP emulator or a WII emulator.

You can also play it with a PS3 or an Xbox 360. If you have an Xbox Series you can play it by backward compatibility.

Silent Hill Homecoming -> You can buy the game on Steam (PC), but you need to patch it.

Silent Hill Origins -> You can play it with a PSP emulator (PPSSPP) or a PS2 emualtor.

Again, you can choose between the PS2 version and the PC version.

Silent Hill 4 -> You can buy the game on Gog.com.

Silent Hill 3 -> You can choose between the PC port (download from MyAbandonware) and the PS2 version (PCSX2).

Also consider that for the PS2 emulator to run smoothly you need a decent PC. You can also play it with PS2 Emulator (PCSX2), you can find the ps2 game on CD Romance. Download the PC game from MyAbandonware and install the Enhanced Edition mod. It runs smoothly even on very old computers.

Silent Hill 2 -> the best version is undoubtly the PC one.

You can also play it with a PSP, PS Vita, PS2 and PS3.

Silent Hill 1 -> Play it with Retroarch (windows, android) or OpenEMU ( for mac users ).

Silent hill on vita download