Either ... or plus is/are

[Planetypus]

Either he or she is going to the party.
Either he or we are going to the party.
Either we or he is going to the party.
Either they or we are going to the party.

Is there any error among the sentences above?

In Either A or B form, does B always become the subject of the following verb? I think yes.

Please explain to me, anybody. Many thanks.

[Mister Micawber]

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Yes, all are OK and your rule is correct.
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_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mister Micawber