This is madness. It shouldn't be given time or consideration.
Walk into any family court and you'll be told that the welfare of the child is paramount. Where are the best interests of the child which currently doesn't and need not exist being served by creating a 'designer baby' so that the grandparent/s can attempt to uphold the whims of a young teenager? Or maybe even to attempt to replace their deceased child?
If this goes ahead can you imagine the precedent it will set? Would it be acceptable for a court to allow this if a deceased donor had lost their life to a genetically related condition?
There are considerably more questions than answers and the cause appears to be the dredging up of the wants and whims of a 14 year old kid, now forever set in stone from the parent's pov because that kid never made it to adulthood. It's desperately sad for the kid's family but no way should their grief be the driver in a quest to re-create what they've lost or fulfill the wishes of an already confused youngster, made at an age where so many grow up to completely change their minds about their plans for the future.