Hello Rebecca,
Thanks for reaching out.
>> I'd like to be able to select a relationship to other listing entries in the front-end post form.
>> How do I integrate the fields into a front-end post form?
You can follow this reply to add the relationship meta box to a front-end form
https://support.metabox.io/topic/front-end-form/#post-47960
and our documentation https://docs.metabox.io/extensions/mb-frontend-submission/
>> How can I save my bidirectional relationships in the field groups?
It isn't possible. The relationship saves data to a separate table wp_mb_relationships.
https://docs.metabox.io/extensions/mb-relationships/#database
>> Which field do I select for this in the WSForm plugin, and how do I set it up?
It is beyond our scope of support. Please contact WSForm support to get further assistance.
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