ASD can't turn into a personality disorder, it's not correct to say that.
Someone with ASD could have a personality disorder as well though.
Having ASD isn't some kind of shield against developing other problems, same as anyone could develop them.
I suppose if someone has both ASD and PD it's difficult trying to separate out what is symptoms of what. But to us on this thread that's unnecessary nitpicking.
The issue for us is that the behaviour causes harm, regardless of whether it comes from someone with ASD, someone with a PD or someone who has nothing medically wrong with them but is just an abusive arsehole.
People also have a personality, as well as any medical conditions they have. None of us are perfect in this world, we all have personality flaws. These people's personality flaws are causing us on this thread harm, that's why we're here.
So trying to figure out if they ought to be diagnosed with something is a misdirection of energy IMO. That's energy we could be using to sort out our own behaviours, lives and futures, all of which is entirely under our own control.
Lots of us on this thread say our relatives are narcissists, but it's just shorthand TBH, we don't know it's true, they haven't been diagnosed with NPD and likely never will be. But they're displaying behaviour that's commonly displayed by narcissists. Whether that's just a narcissistic person with some negative personality traits or someone with actual Narcissistic Personality Disorder. So it's far easier to type "narc" and have everyone understand what you mean, than it is to type "nasty person who may or may not have a medical problem" each time we talk about them. Calling them a narc is just a useful shorthand for communication purposes. There's no need to get bogged down in the details of what they may or may not qualify for a diagnosis of, it's totally pointless.