Objects not fixated and wobbling or floating around too high. Any ideas for solutions?

Hello!

I've pretty much reached the end of the road here. We have created a car experience but having trouble fixating the vehicles (when you move they move) when the idea is that they should stay put. Also when setting pivot to bottom after align selecting, setting the y axis to zero the cars appear way to high and nowhere the ground which seems to be surface detecting just fine. 

Anyone have any ideas here? Would be highly appreciated