The way I could see something like this playing out would be…
Cora takes Henry’s heart before they’re married, so she can force him to marry her, which explains why such a sweet, docile man ended up marrying such a horrible woman, (I’ve always been baffled as to how he ended up falling for her, but that would explain it). Cora goes to Wonderland, becomes QoH, and decides that she needs somewhere to stash her own heart for safekeeping. So she kidnaps her husband who has a vacant chest cavity, sticks her heart in him, then shrinks him, and locks him, and her heart, up in a box. Regina is obviously aware that her father has been kidnapped, but isn’t necessarily aware that he was then given her mother’s heart. That would mean that when Regina killed her father and tossed “his” heart into the fire, she essentially sacrificed both of her parents to enact the curse.
Of course, then you’ve gotta wonder how Cora could still be alive if her heart got tossed in a fire, but, ya know, she’s freakin’ Cora QoH, so I wouldn’t be surprised if she had enough power to get around that somehow.