they are indeed in the same egg group.
https://bulbapedia.bulbagarden.net/wiki/Amorphous_(Egg_Group)

Zekana said in comment #2583286:

they are indeed in the same egg group.
https://bulbapedia.bulbagarden.net/wiki/Amorphous_(Egg_Group)

Indeed, the Grimer and Ralts lines have shared an egg group since the latter was introduced. In fact, Ralts & co. were only added to the Human-Like egg group (alongside the Machop, Drowzee, and Buneary lines, among others) relatively recently, in Sword & Shield.

Alanis, poisoned by a Muk

That's... one way to get a Ralts with Disable and Memento.

Alanis_the_Evoker said in comment #2583287:

Indeed, the Ralts lines have shared an egg group since the latter was introduced. In fact, Ralts & co. were only added to the Human-Like egg group relatively recently, in Sword & Shield.

I mean IMO if we're seeing at it at a biological level, wouldn't their categories somewhat make sense? Since technically the lineage could partially be Faes or beings of light (taking on the appearance of what "we" see, albeit with some mass as well), not human-like literally, but 'shaped as'. Their interior/skeletal structure might not even be present
Or maybe it's just me