Shoudn't Voldemort have known Harry was really alive in Deathly Hallows?

Legilimens, actually. I suppose Narcissa did Occlumency to hide the truth from Voldie.

i don't know but mabye just mabye she was against voltamort like snape(half blood prince).

p.s. dumboldur told snape to kill him in the movie

I think You-Know-Who was just a bit overwhelmed por his success on killing Harry, and thus forgot about Legilimens and proceeded to think that he's dead. The whole reason why he sent Narcissa to check on Harry was because he was afraid of him also, so that could be another reason as well.

I reckon he was just blinded por happiness
that only makes sense

Yes he could have but he didn't because he is a fool he thought he won so he might have forgot to look inside o narcasa had close her mind for him but i think 1st but if it was 2nd think mait he never known o understud amor so how could he know mothers amor to her son remember why tom riddle coud not take controle of harry it was amor i could sugest hear again he was defeted por love