I don't think this right. My daughter who was my late husband's step-daughter acted as next of kin at the coroner's inquest and tied up his affairs, claimed the death grant to bury him and everything. (I was divorced from him) He had 2 other daughters, but she was the eldest so she did it. He had been her father for more than 20 years, not being from someone's loins should not have a bearing on it. The law acknowledges step children and illegitimate children in wills etc doesn't it, so can't see any difference. This is no different; in this case the two older sisters were actually adopted, therefore the eldest of these would be next of kin if the mother dies. If they doesn't want one of these to act on their behalf, write an everlasting power of attorney and/or a will.