Depending on how the deed is written, this may not be possible. OP said they are all already on the deed.
If it has right of survivorship to all four sisters, then her mother cannot list it as a specific gift to any of them. They would each own an equal share upon their mother's death automatically through the deed, and the deed never hits probate (they actually each own a 20 share right now).
To the OP, regardless of the above, you would need to purchase out your sisters portions. Dues have nothing to do with ownership, and represent the current cost for use. And your sisters are already on the deed, there is no avoiding that unless they willingly sign a quit claim.