I have chain bred all the Pokemon on my team and used a hidden power calculator to manipulate the ivs to get the preferred HP type. But when I go to the checker he says that all my Pokemon in my party would have a dark type HP why is this? It totally threw me off and I'm confused now.
Your Pokemon seems perfectly normal. Unless your game is glitched, which it probably isn't since that rarely happens, all your Pokemon may just have odd-numbered IVs.
Hope I helped. :)