That is super courage and trust in God. I will pray for your family.
St Gerard, pray for us.
My daughter had hydranencephaly, which is I presume probably a similar condition. I was told she wouldn't even live long enough make it out of the operating room, and was strongly pressured by both the physician and my ex-husband to go ahead and abort, that it would be kinder, better for me, etcetera.
She lived for 2 hours, and even tried to cry. I held her, my family held her, we put her in a beautiful christening gown my mother had made. She was blessed by many different people. She died right before the time the ethical committee had said we would have to begin life support measures, as my mother sang her a lullaby.
I would be happy to talk with you or your daughter or whoever needs to talk to me. Message me and we can sort out how to communicate off-site. I have "been there" and I can tell you I do not regret carrying my beautiful daughter as long as I could, holding her, and knowing that she knew only love. There are some practical issues about the delivery I can share insights into if you need me to that might be helpful.
I have a friend who is Buddhist and told me that perhaps she was a child who needed a life of only love this time round; I had a nursing Sister tell me that G-d had decided this child should be blessed with a life filled only with love. Then later, a Jewish friend told me that G-d's ways and paths are unknown, but that by giving my child a life filled only with love I had fulfilled a great duty to the Lord. None of these explanations helped at the time, but I find it amazing that three people who never met each other told me something so similar.
I will pray for your family, and know that you do not walk alone. Go to http://www.glowinthewoods.com if it is still there, even just reading other people's stories will help sometimes. Blessings to all of you.