I have a model which inherits "res.partner" (Patient) and this model have a One2many field with the Patient family members (family members are Patients to), and here is the problem.
In the dopdown list I can select other patients to add as a family member, but every time I add a new family member the stored family member is always the patient to which I am adding the relatives.

Does anyone have any idea why this happens?

Code:

# Patient Management
class HealthcarePatient(models.Model):
    _name = 'healthcare.patient'
    _description = 'Patient information'
    _inherit = ['mail.thread', 'mail.activity.mixin']
    _inherits = {
        'res.partner': 'partner_id',
    }

    partner_id = fields.Many2one(
        'res.partner',
        string='Related Partner',
        help='Partner-related data of the patient',
        required=True,
        ondelete='restrict',
        index=True
    )


    family_ids = fields.One2many('healthcare.family', 'patient_id', string='Family')


# Family Management
class HealthcareFamily(models.Model):
    _name = 'healthcare.family'
    _description = 'Family Information'
    _rec_name = 'patient_id'
    _order = 'sequence, patient_id'

    patient_id = fields.Many2one(
        'healthcare.patient',
        string='Patient',
        domain=lambda self: self._get_patient_domain(),
        required=True,
        ondelete='cascade',
        index=True
    )
    relation = fields.Many2one('healthcare.family.relation', string='Relation', required=True)
    age = fields.Char(related='patient_id.age', string='Age')
    sequence = fields.Integer(string='Sequence', index=True)

    def _get_patient_domain(self):
        parent_id = self.env.context.get('parent_id')
        return [('id', '!=', parent_id)]


# Family Relation Management
class HealthcareFamilyRelation(models.Model):
    _name = 'healthcare.family.relation'
    _description = 'Family Relation'

    name = fields.Char(string='Name')