My buddy parked in my driveway under the carport, later at night and he has a black car (hard to see). So I told him to move the car because it's my sisters spot. I didn't force him to move I just told him to move the car. About an hour later when my sister arrived she backed up into his car, just a small dent was left in his bumper. But now he wants her to replace everything on the rear of the car, the bumper the plastic on top and bottom which have no damage. Who's fault is this.

It's private property and I told him to move the car, would it be my sister's fault or his for not moving his vehicle.

I forgot to Add, he didn't move his car after I told him to.

It is your sisters fault, she hit a object that was not moving.
Although he should have moved it, since he was asked, he had no real obligation to move the car. Rules of driving do not change, just because it is on private property. The difference is that in most states the police may not issue a ticket on private property.

As to what to pay for? Get three estimates from professional body shops, and or just allow her insurance to pay for it. Your best option as friend and brother, just stay out of it, and let them have the argument.

Also, if he ? If your friends wants to pay for more than is actually damaged just let him do it? If I read this right, But personally, if I had my bumper dented, normally, if the car made like mine, I would have the plastic replaced also.

I disagree, because it has nothing to do with motor vehicle laws.
It's simply a case of damage to any item belonging to a guest on your property.
I could see this going either way in small claims, because you told him to move his car. BUT you didn't throw him off your property for not moving it, and you were aware of the danger or you wouldn't have told him.
I can see a judge making you split it.
Save the filing fee and time and work it out.

The driver bears responsibility, and liability and best let mechanics, and insurance companies handle it. The rest is just human emotional BS.

I agree 3 estimates is a good way to go about it, but the insurance company has the last word.

This is actually a hard one. Since his car was on your property you may be liable (or your insurance) for damage to his personal property. On the other hand, on that basis, he could bear some responsibility because he did not move the car.

Your sister bears some responsibility because, no matter what she didn't look where she was going.

The best thing is to report it to your homeowners insurance and your sister to report it to het car insurance and let them handle it.

If you want to avoid an insurance claim then do as was suggested, take it to a few body shops to get an estimate. Then split the agreed on estimate three ways.

...
If you want to avoid an insurance claim then do as was suggested, take it to a few body shops to get an estimate. Then split the agreed on estimate three ways.

I don't see the OP indicating that either OP's buddy or the sister has auto insurance. If she does have comprehensive coverage, her insurance carrier should pay (except for the deductible, which she will have to eat and possibly file against the OP's buddy's insurance; or sue the buddy in small claims court). If she doesn't, She can file a claim against the buddy's car insurance.

Also, there is no mention as to whether the sister's car sustained damage; the OP's buddy is claiming damage. Similarly to the preceding paragraph, he would claim against the sister's insurance. If she has none, he would have to sue her. She should insist that (as others have mentioned), he get three estimates, and offer to pay the lowest. As discussed below, she is probably liable; although her brother's buddy seems to have assumed the risk of damage (and comparative/contributory negligence will also apply).

OP is not liable to buddy, who assumed the exact risk of the harm to his car that did occur. An informed homeowner's carrier would properly refuse to pay a dime. However, OP's sister (unless excluded as a resident) could file a claim against OP. I see possible liability on OP's part: failure to be serious enough about getting his buddy to move; failure to turn on the porch light (if there was one); etc. But the chances are that, if they have homeowners' insurance, the policy will provide that the sister, as a resident, cannot make a claim under the policy. Obviously contributory negligence (if it is a complete defense in the jurisdiction) or comparative negligence would work against the sister's claim against OP: she should have made sure she could see where she was going.

First, the damage to the buddy's car would be covered under the sister's liability coverage, not the comprehensive. The comprehensive would only be used to cover damage to her car.

If sister is a resident, then I think damage that she causes to the personal property of a visitor, might be an issue for the OP's homeowner's insurance liability. If the buddy were to file suit, I believe he could make a case that the OP's liability insurance would cover.

... If the buddy were to file suit, I believe he could make a case that the OP's liability insurance would cover.

Sure. But I would argue that it would have to be OP's negligence. I don't see any negligence on the part of the sister as a homeowner. And the homeowner insurance carrier will attempt to shift her liability to her auto insurance carrier, I believe.

Probably, but it still a possibility and a hassle.