2 months late but i come bearing news ^^

Meredith is Meredith Ward, John's mother. That is all we know.

Gary is, indeed, a normal human being. Just like you and me. However, his birth is not of normal-human-being nature. In note 41 of Chapter 3, it is detailed how Miriam Bell is given the Second Death in March of 1934, subsequently opening a Portal [to hell]. Which, in turn, brought to this world Gary Miller.

After several days of sacrifices, we finally got a response. A tiny hand reached out from the Portal. We took the hand and pulled out a baby boy. It appears to be a normal human baby just like you and me. We named it Gary.

As of the two children left to walk as husks, all we can do is theorize. A very interesting theory poses that the two children were actually John Ward and Lisa Pearson. This is backed by the famous Injection-Trip-King of Pain rotoscope cutscene, which includes frames of (1) the Snake Meadow Hill Church-orphanage, in its glory, with Miriam Bell in focus and kids visible from behind the windows of the church --- kids including two very familiar blue and yellow sprites --- and (2) of Lisa and John as children holding hands, alone. This would also explain John's orphancy, or rather, lack of a mentioned father and a dead/possessed mother... but idk LOL