After the death of their baby, the young father believes he can still hear and see his baby however his wife does not share his hallucinations which will bring a brutal end to their relationship.

Remind me of "Don't look now", an old movie with Donald Sutherland.
Her is the link in imdb: http://www.imdb.com/title/tt0069995/
After the tragic death of their baby, a young couple drift apart when the grieving father lose himself in hallucinations and psychic appearitions.

The verb "believes" dilutes the impact of the father's condition, best to word such that for the father the delusions are real rather than a belief.

Another thing about the logline is the vague description of the result i.e; "...brutal end to their relationship."
It seams like your trying to say they kill each other but a brutal end to a relationship could also mean a nasty divorce depends on the individual.
Point is because this is vague the stakes are not clear and best to clarify the stakes in a logline.

Lastly the story is about the parents but neither have been specified as the MC perhaps choose one of them as the protag and the other as the antag. Then pin them against each-other and describe the specific action the MC will take in order to achieve what ever it is they need to for a clear goal.