Can a sibling who grew along claim property rights?

Hello! My friend, who is a single daughter to their parents (biologically), had an elder brother whom her mom had brought up. So, this boy came under my friend's parent's care even prior to her birth & the boy grew with my friend for several years as an elder brother (not sure exact number of years, but almost 15-20 years as I understand) & then he left after his adulthood to his biological parents. Meanwhile my friend also grew up & after he left she is the only one who lived her parents. And her parents settled their property internally to their daughter (Her dad settled to her mom first and then her mom settled it to her in a gap of a few years between each of these transactions). Now, we are trying to understand if there is any chance that they can claim any legal rights over the settled property from my friend. I am not sure if this is to be called as an adoption, since there were no documentation or legal adoption that was involved, it was more informal & verbal as I gather. Could you please advise if there could be any legal issues that they could create?