This case-insensitive code system https://www.ehealth.fgov.be/standards/fhir/CodeSystem/cd-contact-person defines the following codes:

Code	English (English, en)
father	father
mother	mother
child	child
spouse	spouse
husband	husband
partner	partner
brother	brother
sister	sister
brotherinlaw	brother-in-law
tutor	tutor
notary	notary
lawyer	lawyer
employer	employer
grandparent	grandparent
son	son
daughter	daughter
grandchild	grandchild
neighbour	neighbour
stepson	stepson
stepdaughter	stepdaughter
stepfather	stepfather
stepmother	stepmother
sisterinlaw	sisterinlaw