Detect Evil and Good states:
you know if there is an aberration, (etc.) within 30 feet of you, as well as where the creature is located
It says "an" and "the," which are both singular pronouns.
But what if there's more than one such creature? Do you detect them all? Just one? If just one, which one?
The presence of singular pronouns might seem to indicate that you would only detect one however I would argue that you detect all in the area. This has been the case in previous editions and there is no guidance as to which evil/good you would detect if there are multiple (which one might expect if you only detect one, something along the lines of "if multiple sources of evil are present the source with the highest level is detected").
TSR and by extension Wizards has always had issue with wording in spells and it always comes down to the DM's discretion. That said, given the text and literal meaning of "Similarly" if you took it in context that you could only detect one at a time you would similarly only get to detect a creature OR consecrated ground.
Given the fact that it is blocked by enough things not to matter much in a dungeon setting and has short enough range to not matter much out of doors I would say it is not broken to have it detect all in that range and both consecrations and creatures as well. Limiting it to one is probably against RAI and is pretty detrimental for spending a use or slot to cast it.
RAW, it would appear that you can only detect one at a time (I could not find any relevant text to suggest which one, perhaps GM discretion).
However, given how otherwise similar the description of Detect Magic is, I think it would be reasonable for a GM to rule that Detect Evil and Good would work the same way, i.e. "If you sense [Evil/Good] in this way, you can use your action to see a faint aura around any visible creature or object in the area that..." is Evil or Good, as relevant.
