This is about questions in which the OP wants to parent their sibling, despite not being in a parenting relationship, e. g. because the parents still have custody.
We do allow such questions, when the OP (soon) has custody of their sibling, e. g. a recent example. However, when the OP is not acting in loco parentis, e. g. because they disagree with the way their parents parent their sibling, these questions usually get closed. (I also sometimes come across old questions by a sibling that are not closed, for example.)
How to deal with questions, in which the OP wants to parent their sibling, despite not being in a parenting relationship with them?
I didn't find an appropriate prior discussion, so I thought it would make sense to bring this up, after seeing the responses to this meta question about a special case (keeping such a question open by pretending to be the sibling's parent).