Will sin befall the questioner and her sisters for their participation in attempting to abort the fetus of her niece?

It is not permissible to abort the fetus at any stage of its life, especially after the ensoulment, except out of necessity. Approving of and assisting in abortion is a sin, and all who participated in it must repent, in accordance with the Almighty's saying: "And do not cooperate in sin and aggression." If the abortion occurs after 120 days (i.e., after the fetus has been formed), then whoever carried out the abortion must pay the blood money (diyah) of the fetus to its heirs, which is one-tenth of the mother's diyah. Girls must also be protected by obliging them to observe proper Islamic dress (ستر), avoid forbidden mixing, and unlawful seclusion, in accordance with the Almighty's saying: "O you who have believed, protect yourselves and your families from a Fire."