Now it's possible once Stephan turned human the rules changed
Stefan force the Realtor to change the name to the deed and then invited Stefan it .
Stefan's change to human did not affect the ownership of the house .

because Vampires don't need an invitation into another Vampires house. That is why they are always compelling the owners of homes and then stays with them. Then will tell the owner to let them in.
Now it's possible once Stephan turned human the rules changed and they were just in a different house. But that's how it would have been if Stephan was still a vamp

That make sense , Bonnie just put Enzo's body in her car , and drive all the way back to Mystic , and put him in another house for better scenery .
And by the way , how many house doesn't Bonnie have ?
she bought that house ( the one Stefan had cancel the deed) with her father's money , and Bonnie can only invite her mother into the house if she also own the the other house

Wasn't it a different house? I got the impression that by that time Bonnie had left the realtor house and was back in the Mystic Falls house.
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Bad writing

We never actually saw Abby in the house though. Bonnie went outside to her.
I only dance at the funerals of people I hate

Good question. Bonnie is no longer the owner of the house,therefore she should not be able to invite her mother in.
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They were in a greenhouse of some sort. Perhaps the invitation is only good for the main house?