Its depends on that person's religion. If they are Christian then you call them Christians, if they are Mormon then you call them Mormon's. Whatever their religion is that is was you call them. Hope this helps you.
By their name, and if they tell you of their faith, the name that coincides with it, e.g. Christian, Muslim, Buddhist, or so on. A word to describe people of any religion that are very religious is "pious".
If they do not profess a religion, they are call Atheists or Agnostics.
If they profess a religion, but do not practice it, they are called non-religious (e.g., non-religious Jews, lapsed Catholics, etc.).
People who spread religious ideas are called missionaries.
People who are not sincere are called dishonest and untrustworthy. People insincere in religious beliefs are called hypocrites.
missionaries
They could be called Preachers.
they are called dissenters
the sign of the cross
Those are known as "martyrs".
Well the people were called Celts and their religious group were the Druids.
these people were called the Puritans.
Religious oppression is one term.
People who believe in Judaism are called Jews.
Religious settlements established to convert people to a certain faith are called missions or missionary settlements. These are typically founded by religious organizations in order to spread their beliefs and teachings to new areas and populations.