And the ironic thing is that the Mom would STILL be just considered MID at best on the scale of bad anime parents !!
I'd say low-mid, if not outright on the low end- though leaving out the ones that are
supernaturally bad (ie literal villains, evil magic warriors, demons/monsters/etc). Even genuinely abusive parents at least taught their kids how to
function, even if it came with the addition of a whole lot of baggage or a twisted world view. She literally didn't care enough to actually raise her kids or even look after them. She didn't teach them or support them in any meaningful way. Frankly it's a small miracle they didn't grow up into sociopaths or end up half-feral.
Also, bravo on the mangaka for making them both the MC and FMC much more human. The FMC is shown with moments of weakness and humor at her expense, helping to emphasize that for all her sadism and sensibility she's also plenty in love with the MC that causes her to sometimes stumble as well. Meanwhile the MC is given a sympathetic reason for being the mess of a person he is: he isn't someone who just coasted through life and now has neither the academic or emotional intelligence to function in adult society,
he and his sister literally all but raised themselves. And then he sets out on his own to support his sister's dream, hoping that in success she'll find stability that will give him piece of mind.
Poor dude was essentially forced to skip half the tutorial and was thrown into Hard Mode right after.