What is the correct subject pronoun for the planned trip?

The correct subject pronoun for the planned trip is "we" because it indicates that the speaker is part of the group involved in the trip. In this context, "we" is used as the subject of a verb, representing the collective aspect of planning and participating together.

For example, if one were to say, "We are going on a trip," the use of "we" clearly shows that the speaker and others are taking action together. This pronoun is essential in expressing that the planned trip involves the speaker's group as active participants, thus making it the appropriate choice.

In contrast, "us" is an object pronoun used when the group is receiving an action rather than performing it; "they" and "them" refer to another group or individuals who are not part of the speaker's group, which would not fit in the context of planning a trip involving the speaker's group.