Can you legally bury a person under your house?

Yes that would be considered Home Burial

In most states it is actually legal to bury your loved one on your property but there are a number of things to consider. There are several agencies in the United States that exist with the sole purpose of helping families that wish to do home burial. You can engage the services of a death midwife who will help you make the proper arrangements for home burial of a body. A death midwife in the state of Oregon is required to be licensed and only six states across the US require that you have involvement from a funeral director. The sole purpose of the death midwife is to make certain that any steps you may not have thought of during this time of grief are taken care of and that the burial of the body is done with dignity and within the proper standards to ensure the safety of the body into the earth. Please note it is necessary to obtain local consent from your local authority before burial can take place.

Sure, why not. People have their loved ones' ashes in their homes. Our grandma is sitting in a rocking chair in the attic.

If done so by the laws of your locality, sure. In practice, no, that won't be allowed.

no. dear you must follow city ordinances.