She found an abandoned baby and wants her daughters to breastfeed him so that he will become a mahram for her
Question

                A neighbor of ours found a few hours old baby. She fears for him from the mistreatment of the orphanages. She wants to bring him up, but when he grows up it will be haram if he stays with her alone in the house. She says that if she brings him up like she does with her own children, she will not able to leave him. She has married daughters and they have babies. Shall she ask her daughters to breastfeed this baby so that she becomes his grandmother through breast feeding? And so it will not be haram if he stays with her at home. Or this will be considered a disliked trick? 

My mother has breastfed a daughter of our neighbor with my older brother several times. So she became a sister of my brother (of breastfeeding). Has she and her sisters become sisters for me as well or sisters for my brother who was breastfed with her only? This question is to specify the limits of my dealings with them, are they considered my sisters, or strange women to me?.
Praise be to Allah.
    If one of your neighbour’s daughters breastfeeds this child 
    for five feedings, he will become her son through breastfeeding (radaa’ah) 
    and your neighbour will become his grandmother through breastfeeding, and 
    all her daughters – the neighbour’s daughters – will become his maternal 
    aunts through breastfeeding. Thus she will become able to raise him 
    throughout his childhood and beyond with no problems, because he will be a 
    mahram to her. 

    This is not regarded as a trick, rather it is a legitimate 
    shar’i solution which will enable this woman to raise this child and take 
    care of him, and there is the hope that she will be rewarded for that by 
    Allaah. The Prophet  (peace and blessings of Allaah be upon him) said to 
    the wife of Abu Hudhayfah concerning Saalim, the freed slave of Abu 
    Hudhayfah: “Breastfeed him, then you will become his mahram.” Narrated by 
    Muslim (1453). 
And Allaah knows best.