Can a girl and a boy become temporary siblings through a formula?

In Islam, there are only two forms of siblinghood: by blood and through breastfeeding. There is no formal contract of brotherhood or sisterhood, and no such arrangement can establish the status of mahram. Anyone who claims otherwise is an innovator and is to be condemned.

In general, however, every believing woman is like a sister and a mother to every believing man, while all the boundaries and considerations that apply between non-mahrams remain in force.