That's because all 3 accs are using the same saved_games game data, including settings.json. You need to use a low hd mod for the filler accounts and have the modinfo.json file point to a subdirectory within saved_games/D2R. If you have a discrete graphics card, the low hd mod accs should only be using ~1gb RAM btw.
Someone told me about having different subdirectory but forgot all about it.
I can do 4 + 1 on steam and all on low, everything off, with the steam account now being my main. 5 will have random crashes, 3 + steam is fine.
I can’t do 3 on my 5600x/7600xt even when using steam without crashes.
But, I have an i9 13900f 64gb ram and 1x2tb and 2x1 tb nvme, although one is windows 10 that I haven’t got around to wiping.
I run a rx 6800 and it’s surprisingly ok with it.