Holes in the brain

A good friend of mine has 4 children...2 of which are severly disabled. The boy is soon to be 12 and his sister will be 11. When the boy was born he was "normal" (as in no deformities, diseases, disorders, etc), but when he was around 6mo old the parents started to notice something wrong. Instead of progressing as a baby should (crawling, holding head up, rolling over) he started to regress and by the time he was 14mo he was back to infantile. After many tests it was found that the boy had/has "holes in his brain" but the doctors have not been able to  determine any cause for the problem. During the time of going from doctor to doctor the parents got pregnant again with a girl. All of the pre birth tests were performed, including an amniocentesis, nothing was found. Feeling comfortable the parents had the girl and for the first year everything was good. The girl was progressing, talking, mimicking, stranding on her own, etc. Around 14mo (much later than the boy) the parents started noticeing the same things, regression. They took her to the Dr. whom told them they suspected she was deaf, but her ears were fine, then blind, same thing (eyes were fine). Within a few short months the girl lost everything she had learned and it was discovered that, just like her brother, she had/has holes in her brain. Both children are complete and total care, they wear diapers, can't hear, speak, see, and have to be fed a special diet. They can feel touch. Fast foward several years and it's not suspected that the boy is going downhill quickly following a several abdominal hernia and sugery, and now they think that whatever is "eating" his brain is back after a hiatus and is moving quicker than before.
If you know someone that can help or have any clue what this could be PLEASE point me in the right direction. The father is watching 2 of his children slowly die, the boy sooner than expected. The doctor's have NO CLUE what is wrong with the children. The couple has had 2  other children since and they are fine, without any copmlications or disorders/disabilities.
The disabled children were also dilvered differently (boy was natural-no drugs, and the dughter was C-section) the pregnancies were without complications and all the tests didn't show anything.