Also, I'm sure you're beating yourself up over this already right now, but Reincarnate is kinda a terrible / gamebreaking spell. There's a reason Lizardfolk have 2 Humanoid HD and 1 LA; even though it's a bit excessive, these are to counterbalance the numerous strengths and bonuses a lizardfolk gets, especially the massive natural armor and secondary bite attack.
Dragon Disciple is already a strong class with a D12 and numerous stat boosts (if you're keeping core) and although it may seem reasonable to swap out the stat boosts for spellcasting progression, bear in mind that spellcasting, even sorcerer spellcasting, is probably the strongest class feature in the game by a large margin. Even 1/2 spellcasting on a d12 prestige class is pretty strong.
That being said, bear in mind your group chose to make him the front-liner, and his drawbacks (in terms of terrain, reflex, and disables) should serve to make life difficult enough for him that everyone is involved.