Aw, you're just a bundle of raw nerves, aren't you!?
Don't work yourself up too much over this!
First of all, you should have nothing to fear! If there are actually ghosts none of them have done anything malicious, all they seem to have done (if what everyone's seeing are ghosts) are walk past you guys. And if you're that concerned, not to sound silly, why don't you see if there are any paranormal societies by you and have them check out your house? That might really help you!
I would be inclined to believe that you house is not on a burial mound. Only because I'd think any mounds a tribe may have made would be close together, not miles apart. At least that's my experience in the mounds I've visited.
By the way I'm no expert, I base my opinions on watching Ghost Hunters on SciFi and a paranormal investigation I participated it/walked around with a few weeks ago.
I just don't want you freaking out and getting yourself sick about this!