They are required to give the info. They can fill information that they know e.g the Names, DOB, country of birth. Under marital status if they do not know, fill in unkown (will explain why it is unknown in LOE). Address they can enter the country and city if known.
Thank you for this. Do you have direct experience of it when applying? Relationship breakdown is putting it mildly. The parents of the applicant (my partner) are Muslim. I'm not. So everything has to be done in secret, as they will not consent to giving any such information and would do worse if they knew it was being given without them knowing. We will certainly write up a LOE.
Well put. Just to note, it's the principal applicant (and the sponsor, partly) that needs to provide this information. For mother and father, it's just date of birth, country of birth, address, and marital status. (They do ask for email, but I didn't even bother adding an explanation about not having one, not really expected for parents).
