My wife’s brother is in his 80’s and when anything happens to him I would like to know who is his next of kin and who is responsible for sorting out his affairs. He is a widower and has a step-daughter, although we don’t know whether he legally adopted her. As far as I know he hasn’t made a will.
If your brother-in-law hasn’t made a will the question of whether he formally adopted his step-daughter may be crucial. A child adopted by a married couple is treated by the law as if born as a child of the marriage. So if the step-daughter was adopted she will be your brother-in-law’s next of kin. If not, she is unlikely to have any claim on his estate unless she can show that she was being maintained by him prior to his death.