Does Bless Require Line of Sight?

Question

I was the DM in a game last night and the scenario was thus:

The healer on the ground floor of a tower wanted to cast Bless on her companions the floor above. This floor only had one access point, a trap door which was closed. I argued, that since they were behind total cover as per PHB 204:

A target with total cover can’t be targeted directly by an attack or a spell, although some Spells can reach such a target by including it in an area of effect. A target has total cover if it is completely concealed by an obstacle.

that bless would not work, her opinion was that since in the spell it mentions blessing up to 3 creatures in range. that the cover rules would not apply as you are not targeting a creature but a point between the creatures.

You bless up to three creatures of your choice within range. Whenever a target makes an attack roll or a saving throw before the spell ends, the target can roll a d4 and add the number rolled to the attack roll or saving throw.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, you can target one additional creature for each slot level above 1st.

Is either of our rulings correct?

Answer 1

You are targeting each creature

The spell, as quoted in your question, refers to each creature as a target (PHB 219, emphasis mine):

You bless up to three creatures of your choice within range. Whenever a target makes an attack roll or a saving throw before the spell ends, the target can roll a d4 and add the number rolled to the attack roll or saving throw.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, you can target one additional creature for each slot level above 1st.

The rules for total cover (PHB 196) apply, you cannot target creatures completely concealed by an obstacle.

This wouldn't work as an area of effect either

Even if the above was incorrect, or if you ruled that bless does work as an area of effect spell from a point (as your player suggests), this still would not work. The rules for targeting continue in the Spellcasting chapter with (PHB 204):

If you place an area of effect at a point that you can't see and an obstruction, such as a wall, is between you and that point, the point of origin comes into being on the near side of that obstruction.

and the section on areas of effect later on the same page reads:

A spell's effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn't included in the spell's area. To block one of these imaginary lines, an obstruction must provide total cover, as explained in chapter 9.