The creation of the relation takes place in a standard way, like all M:M relations.
Once the relation has been created, you can define the type of relation (kinship) between the two records and the status of the relation itself: use the Change additional data button.
The type of relation is defined by the Kinship type and Kinsman type fields. The relation status is defined by the Kinship status field.
Kinship type sets the type for the current record, while Kinsman type sets the relation type for the related record.
Of course Kinship status sets the relation status for both records.