If the house is currently in a trust, then it legally belongs to the trustee(s) of that trust (assuming that the deed was transferred and recorded). If that is the case, then the only way to change who the house goes to is to amend the trust. You didn't say who started the trust, but if it was your grandmother then she can amend the trust by simply having a document prepared and signing it in front of a notary. You should consult an estate planning attorney in your area for more specific information.
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The house will not pass by the terms of the will if it is owned by the trust at this point. To whom the house would go would then depend on who the beneficiaries are under the trust.
This can be modified, but keep in mind that real property can only be legally transferred by deed.
It MAY be possible to do this, but there are not enough facts in your summary to tell. It cannot be done by Will if the house is titled in the trust, as my colleagues have indicated. You need to contact an estate planning attorney to meet with your grandmother and see if she has the capacity to amend her trust. If she does, then this should be a simple change, IF that is what she wants to do. It is your grandmother's choice on how to handle this.
If your grandmother does not have capacity to amend her trust, then I do not think this can be done. If your mother was acting as successor trustee, due to your grandmother's incapacity, and the trust gives her the right to amend the trust, (which would be very unusual), or the power to appoint a different beneficiary, which would be somewhat less unusual, that may also accomplish your goal. There is no way to tell without having an attorney review the documents.
This should be done RIGHT AWAY, given your grandmother's condition. There may be no way to make changes, upon her death.
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If the trust owns the asset, only the original grantor or the trustee can convey interest in the property. I encourage your family members to employ an attorney to assist you in carrying out your mother's wishes.
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