In English "They/Them" is used to describe a group of more than one person that is gender agnostic.
"They went to the park", "Have you seen them at the park"
"It/They/Them" is normally used to describe one or more genderless objects "It" being the singular.
"It was seen in the park", "They were seen in the park", "Have you seen them in the park?"
Calling a person an "It" would be seen as extremely degrading and lacking respect.
Non-Binary parlance says that "They" is to be used in all instances where "It" would otherwise be used.
That is a bit confusion for me to be fair.
"They" is not non-binary in Portugues at all... the translation is "Eles" ou "Elas", it is the plural form depending of the genre.
Non-binary people here are starting now using "Ile" or "Elu" (3rd-person binary) but that is really a big fuck off in either song and gramar so I don't think it will be incorporated to our Language but maybe they will find a better way to create non-binaries pronouns.
Today there is no option in Portugues language like English... there is no non-binaries "It" or "they" here.
Eu = I
Tu/Você - You
Ele - He
Ela - She
Vós/Vocês - You (plural)
Eles - They (feminine)
Elas - They (masculine)
We don't have differentiation between objects/person/animals so Ele/Ela is used to all... no "It" way here... after all Animals and Objects here have genre too... Eg. Machine is an object feminine in Portuguese "Máquina" so you use "Ela"... Clock is an object masculine in Portuguese "Relógio" so you use "Ele".
PS. When I say Portuguese I'me referring to Brasilian Portuguese... maybe there are some differences between original Portuguese.