You can run PS1 via Retroarch, but i don't think it runs well on O3DS, there's also a lot of other consoles emulators in RetroArch you can try it, and of corse you can run DS games via TWiLight Menu++
I tried it in FCEumm and Snes9x2002 and worked fine, first tou have to activate the Netplay Tab, go to Settings - User Interface - Views, then turn the Netplay Tab on
I think Snes9x for old 3ds, I haven't tried on a O3DS Snes9x 2002 core for RetroArch should be good too, and is compatible with Achieviments and Netplay
Create a new folder in the RetroArch folder, then go to Settings-Directory-Thumbnails and select the folder you created. Go to User Interface-Apperance and make sure the Thumbnails are enabled. The Thumbnails works better in RGUI theme.