Exported fbx from Blender

I imported a model to Blender and then exported it to use in Unity,
but every time i export it and other similar models there's always the same problem going on with their fingertips, now they're facing the floor but sometimes it's going upward.
Models are still fine if I just import them to Unity,
but I'm unable to add things that i can do in Blender.
I'm completely new to Blender and Unity so I really hope it is some kind of mistake I'm making while exporting or importing with Blender, I tried uploading the models a few times and every time there is the same problem with or without any packages in Unity.

 

The 2 guesses I have are....

The bones for the finger tips are rotating. Check in Blender, ideally your skeleton should be in its rest position at export. You'd then use animation to drive the skeleton in Unity.

Other guesses is the weight painting is wrong. Vertices are permitted to have a max influence of 4 in Unity I think. This can be lowered but I think the cap is 4 atm.