Model is getting stretched when adding Basic IK(control rig)

Still does not work. I tried to remove all the bones, re-add them inside Unreal and just make it as simple as possible by adding a few bones to the hood-part that sticks out and then re-creating a rig with basic IK but it still messes up. Bones does not have to be all straight, I mean I should be able to make organic skeletons, like an octopus for example?

Are there any good tutorials for how to create custom skeletons/rigging? Almost every tutorial or guide is using a standard human bi-ped skeleton or the Unreal skeleton.