For the Lord's Prayer, I'm sure we learned 'as we forgive THEM that trespass against us' at school, but elsewhere I always hear 'as we forgive THOSE that trespass against us'.
It raises an interesting question: 'them' is the object of the verb 'forgive', and 'those' is the subject of 'trespass'. In other words, the same entity (them/those) is both object and subject at the same time, so a choice has to be made.