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If all of your father's assets were also in your mother's name, I don't see any need to have to spend a lot of money. For instance, if the house was deeded to them both as "joint tenants" it entirely belongs to your mother now. If the bank accounts were joint---same thing.
I would suggest, however, that a lawyer be consulted merely to make a quick check that everything is all right, and to get the deed in order, and make sure that all the "loose ends" are tied up. It would likely be very inexpensive and save a ton of trouble in the long run. It would likely not be a problem immediately, but some time in the near future, certain things would have to be taken care of.
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