Indexing Many-to-many Joining Table

In the following example, I have a "Person" table, and a many-to-many "Relationship" table which stores the r/ship between any two people:

[Person] [Relshp]
---------------- ---------------------
| PersonId PK|<-.-. | RelshpId PK |
| PersonName | '-| PersonId |
---------------- '--| RelatedToPersonId |
| RelationshipType |
---------------------

There are 2 FK constraints, linking

1. [Relshp].[PersonId] to primary key [Person].[PersonId], and
2. [Relshp].[RelatedToPersonId] to primary key [Person].[PersonId].

What kind of index structure would best support those FK constraints?

Would it be:

a) One combined index:
CREATE INDEX IX_Relshp ON Relshp (PersonId, RelatedToPersonId)
or
b) Two indexes:
CREATE INDEX IX_RelshpP ON Relshp (PersonId)
CREATE INDEX IX_RelshpR ON Relshp (RelatedToPersonId)
or
c) Two "mirrored" combined indexes:
CREATE INDEX IX_RelshpP ON Relshp (PersonId, RelatedToPersonId)
CREATE INDEX IX_RelshpR ON Relshp (RelatedToPersonId, PersonId)