My brother recently passed away after battling cancer.Just I know he went through so much emotional suffering and pain .I feel as though between doctors appointments , hospital tests and diagnosis his cancer was over looked firstly by his doctor who did not see the obvious signs of his cancer,the hospital who took numerous tests and told my brother it was an infection ,then to be told he could rule out cancer.then a day before his surgery to remove the large tumour in his neck.it was only then he was told it was cancer . I believe so much more should have and could have been done .Anyway I did complain and I was told to get his next of kin to fill out and sign the forms for access to his medical notes... However I believed that my sister was his next of kin but I was wrong .after she signed and send of the conssent forms.i received a letter from the health board saying my sister wasnt the next of kin and they couldn't take my complaint any further just I think my father may be next of kin but we aren't in contact and so I wont be able to get next of kin .im not sure of exact dates either so what should I do next

Consult an attorney who specializes in malpractice cases.

Reading your other posts it appears you are upset with his medical team because they would not give you the information you requested after your brother asked them not to discuss his care with his family.

If he was married, his wife would be next of kin, then any surviving children if divorced or widowed. If neither of these apply, his next of kin would be any surviving parents.

Just know now that you don't have a lawsuit simply because his medical team refused to discuss his medical condition or treatment.

You should discuss this matter with an attorney because this is a malpractice case.

They can't, they are not the aggrieved person or next of kin.