If probate was never opened, the issue is who was awarded the house in the will? Also what was the value of the property at the time of death? Depending on these answers your mother may have to open probate or you may be able to transfer the property by affidavit. You definitely want to consult with a probate attorney.
I agree with Mr. Brophy. You should go through your files and obtain as much documentation as possible to substantiate your claim, and track the funds. In general, the attorney fees for representing the personal representative are taken from the estate. If you can convince your sister she will be depleting her own inheritance by denying you your funds, you might possibly resolve this amicably. If not, hire your own counsel as soon as probate is filed.
A will is legal if it complies with the statutory requirements of the state in which it was executed. For example, some states recognize holographic (handwritten) wills, while other states do not. In terms of the testator or testatrix, they must be of sound mind, recognizing the extent of their estate, and not be unduly influenced in the making of their will. In order words, the actual will is either legal or not when written, not when admitted to probate. It is only when it is admitted to...
I would start by having an attorney review the trust because there is a possibility that all of your mother's assets are disposed of by the trust. If that is not the case, the will needs to be probated in North Carolina. Any assets in Massachusetts not disposed of by the trust will need to be disposed of through an ancillary probate. Many attorneys will be happy to assist you and get paid through the estate, so that should not be an issue for you. Best wishes.
Probably not. The doctrine of laches is not favored and doesn't appear to apply to your case. Laches is used when a party delays so long in bringing suit that the other side loses it's ability to properly defend against the cause of action. Examples would be when critical evidence is not preserved or key witnesses can no longer be located. Here the only issue would be whether you wrongfully incorporated someone else's music into your own and profited as a result.