In NC, the house is subject to a Medicaid lien. Without special planning, after your father in law's death, even though the will leaves the house to your husband and was drafted and signed before he went to the nursing home, the house will be subject to the lien. Please have the agent under your father-in-law's Power of Attorney, see an elder law attorney immediately. Depending on the circumstances, the house may be able to be protected.
If your father didn't marry his girlfriend and was explicit in his estate planning documents that her right to live in the home was limited to two years, then it is unlikely she will be able to extend her stay. However, if the property was deeded to her or the estate plan extended her rights then you may be in a different situation.
The beneficiary of the life insurance policies should file directly with the insurance company. It would be very wise for you to consult with a probate attorney and make sure that the estate is handled properly. All assets which belonged to your family follow the will or if no will exists, follow the laws established in NC to handle estates when citizens pass. This is a necessary procedure to make sure that all property is clear so that it may be properly inherited.
You can legally add a codicil or write a new will for that matter, but I would strongly advise against it. An attorney is trained to make sure that the document and provisions comply with the law and the court requirements. Failure to handle these documents properly can nullify your existing will. This is not something that you can correct, when years later, it's invalid, because, unfortunately, you are no longer here to correct the situation.
A trust can include all of the information a will includes, so that no probate is necessary and the document will remain private. However, an estate will not avoid probate, even with a trust, if all of the assets are not transferred to the trust name.
Debts of the decedent are the responsibility of the estate, not the children. I would suggest that you speak to an attorney in NY before proceeding further. Often to sell the house the will must be probated, but you should not probate the will in this instance without legal help, because once you become the personal representative, you will have responsibility on behalf of the estate to pay the outstanding debts in the correct order out of the estate.
I would recommend that you use a S.C. Elder Law Attorney, unless you decide to move your parents to NC, so that you would be closer to them. If so, please see a NC Elder Law Attorney to learn the best way to handle this matter in NC.
This is a difficult situation. If your uncle didn't leave legal instructions about his wish to be buried in NC with the rest of his family and his wife wants him buried in Ohio, then he will be buried in Ohio, unless you can convince her otherwise.