Poor little guy. Dang that dog owner. I’m sending love and prayers for the recovery of Jack and the correct diagnosis for his dad, asking the Comforter to wrap his arms around you and your entire family to get thorough the trials ahead.
Kids tend to do OK, depending on the parents’ attitude. I have a nephew who was born with thumb and forefinger separated properly, but all other 3 digits fused. This was true of all 4 limbs.
My S-I-L went the poor baby route and tried to protect him from even knowing he had problems. Lots of surgeries, etc. I would have taught him that things happen and he can do whatever he wants to do.
He still seems to have turned out OK, although I’m sure he was teased when he was young.