If you sign the house over to your sister there needs to be a legal agreement, drafted by your attorney, requiring your sister to pay off the loan prior to the land being transferred. You are not legally obligated to give her the home. All of you have an interest. Maybe it would make more sense to sell the home. Please talk to an attorney I don't have all the facts necessary to help you.
The smartest thing to do is to hire an attorney to represent your interests. The attorney will write a letter to the executor and ask to be apprised of what is being disbursed. The attorney will also be able to watch the court file and the activities of the executor and make sure that your interests are being watched. The attorney letter verses your own letter, has teeth and will bite them if they don't handle the estate properly.
In North Carolina, your only obligation to your brother is of an ethical nature. If your relationship is worth keeping, or if you know that your father really wanted this money split, a gift from you to your brother, of $1900.00, may go a long way to preserve peace. However, by law, an account left solely to you, is yours. This is why estate planning is so important. Families are destroyed over money, when proper planning could have preserved relationships.
It depends on how the deed is titled in NC. If daughter is listed on the deed as joint with right of survivorship with your father she will receive the entire property, regardless of what the will states. Moreover, If it is owned in just her name, it's hers. However, if it is owned any way but this way she will not receive the entire property, but share an interest with others.
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.